Re: [PATCH 1/1] Revert "iommu/iova: Retry from last rb tree node if iova search fails"
On 08/03/2021 16:22, John Garry wrote: While max32_alloc_size indirectly tracks the largest*contiguous* available space, one of the ideas from which it grew was to simply keep count of the total number of free PFNs. If you're really spending significant time determining that the tree is full, as opposed to just taking longer to eventually succeed, then it might be relatively innocuous to tack on that semi-redundant extra accounting as a self-contained quick fix for that worst case. ... So since the retry means that we search through the complete pfn range most of the time (due to poor success rate quoted), we should be able to do a better job at maintaining an accurate max alloc size, by calculating it during the failed search, and not relying on max alloc failed or resetting it frequently. Hopefully that would mean that we're smarter about quickly failing the allocation. I'll further look at that. Thanks, John ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH 1/1] Revert "iommu/iova: Retry from last rb tree node if iova search fails"
On 08/03/2021 15:15, Robin Murphy wrote:
I figure that you're talking about 4e89dce72521 now. I would have
liked to know which real-life problem it solved in practice.
From what I remember, the problem reported was basically the one
illustrated in that commit and the one I alluded to above - namely that
certain allocation patterns with a broad mix of sizes and relative
lifetimes end up pushing the cached PFN down to the bottom of the
address space such that allocations start failing despite there still
being sufficient free space overall, which was breaking some media
workload. What was originally proposed was an overcomplicated palaver
with DMA attributes and a whole extra allocation algorithm rather than
just fixing the clearly unintended and broken behaviour.
ok, fine. I just wondered if this was a theoretical problem only.
While max32_alloc_size indirectly tracks the largest*contiguous*
available space, one of the ideas from which it grew was to simply keep
count of the total number of free PFNs. If you're really spending
significant time determining that the tree is full, as opposed to just
taking longer to eventually succeed, then it might be relatively
innocuous to tack on that semi-redundant extra accounting as a
self-contained quick fix for that worst case.
...
Even if it is were configurable, wouldn't it make sense to have it
configurable per IOVA domain?
Perhaps, but I don't see that being at all easy to implement. We can't
arbitrarily *increase* the scope of caching once a domain is active due
to the size-rounding-up requirement, which would be prohibitive to
larger allocations if applied universally.
Agreed.
But having that (all IOVAs sizes being cacheable) available could be
really great, though, for some situations.
Furthermore, as mentioned above, I still want to solve this IOVA aging
issue, and this fixed RCACHE RANGE size seems to be the at the center
of that problem.
As for 4e89dce72521, so even if it's proper to retry for a failed
alloc,
it is not always necessary. I mean, if we're limiting ourselves to 32b
subspace for this SAC trick and we fail the alloc, then we can try the
space above 32b first (if usable). If that fails, then retry there. I
don't see a need to retry the 32b subspace if we're not limited to it.
How about it? We tried that idea and it looks to just about restore
performance.
The thing is, if you do have an actual PCI device where DAC might mean a
33% throughput loss and you're mapping a long-lived buffer, or you're on
one of these systems where firmware fails to document address limits and
using the full IOMMU address width quietly breaks things, then you
almost certainly*do* want the allocator to actually do a proper job of
trying to satisfy the given request.
If those conditions were true, then it seems quite a tenuous position,
so trying to help that scenario in general terms will have limited
efficacy.
Still, I'd be curious to see if making the restart a bit cleverer offers
a noticeable improvement. IIRC I suggested it at the time, but in the
end the push was just to get *something* merged.
Sorry to say, I just tested that ("iommu/iova: Improve restart logic")
and there is no obvious improvement.
I'll have a further look at what might be going on.
Thanks very much,
John
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Re: [PATCH 1/1] Revert "iommu/iova: Retry from last rb tree node if iova search fails"
On 2021-03-01 15:48, John Garry wrote: On 01/03/2021 13:20, Robin Murphy wrote: FWIW, I'm 99% sure that what you really want is [1], but then you get to battle against an unknown quantity of dodgy firmware instead. Something which has not been said before is that this only happens for strict mode. I think that makes sense - once you*have* actually failed to allocate from the 32-bit space, max32_alloc_size will make subsequent attempts fail immediately. In non-strict mode you're most likely freeing 32-bit IOVAs back to the tree - and thus reset max32_alloc_size - much less often, and you'll make more total space available each time, both of which will amortise the cost of getting back into that failed state again. Conversely, the worst case in strict mode is to have multiple threads getting into this pathological cycle: 1: allocate, get last available IOVA 2: allocate, fail and set max32_alloc_size 3: free one IOVA, reset max32_alloc_size, goto 1 Now, given the broken behaviour where the cached PFN can get stuck near the bottom of the address space, step 2 might well have been faster and more premature than it should have, but I hope you can appreciate that relying on an allocator being broken at its fundamental purpose of allocating is not a good or sustainable thing to do. I figure that you're talking about 4e89dce72521 now. I would have liked to know which real-life problem it solved in practice. From what I remember, the problem reported was basically the one illustrated in that commit and the one I alluded to above - namely that certain allocation patterns with a broad mix of sizes and relative lifetimes end up pushing the cached PFN down to the bottom of the address space such that allocations start failing despite there still being sufficient free space overall, which was breaking some media workload. What was originally proposed was an overcomplicated palaver with DMA attributes and a whole extra allocation algorithm rather than just fixing the clearly unintended and broken behaviour. While max32_alloc_size indirectly tracks the largest*contiguous* available space, one of the ideas from which it grew was to simply keep count of the total number of free PFNs. If you're really spending significant time determining that the tree is full, as opposed to just taking longer to eventually succeed, then it might be relatively innocuous to tack on that semi-redundant extra accounting as a self-contained quick fix for that worst case. Anyway, we see ~50% throughput regression, which is intolerable. As seen in [0], I put this down to the fact that we have so many IOVA requests which exceed the rcache size limit, which means many RB tree accesses for non-cacheble IOVAs, which are now slower. I will attempt to prove this by increasing RCACHE RANGE, such that all IOVA sizes may be cached. On another point, as for longterm IOVA aging issue, it seems that there is no conclusion there. However I did mention the issue of IOVA sizes exceeding rcache size for that issue, so maybe we can find a common solution. Similar to a fixed rcache depot size, it seems that having a fixed rcache max size range value (at 6) doesn't scale either. Well, I'd say that's more of a workload tuning thing than a scalability one - ok a massive system with hundreds of CPUs that spends all day flinging 1500-byte network packets around as fast as it can might be happy with an even smaller value and using the saved memory for something else. IIRC the value of 6 is a fairly arbitrary choice for a tradeoff between expected utility and memory consumption, so making it a Kconfig or command-line tuneable does seem like a sensible thing to explore. Even if it is were configurable, wouldn't it make sense to have it configurable per IOVA domain? Perhaps, but I don't see that being at all easy to implement. We can't arbitrarily *increase* the scope of caching once a domain is active due to the size-rounding-up requirement, which would be prohibitive to larger allocations if applied universally. Furthermore, as mentioned above, I still want to solve this IOVA aging issue, and this fixed RCACHE RANGE size seems to be the at the center of that problem. As for 4e89dce72521, so even if it's proper to retry for a failed alloc, it is not always necessary. I mean, if we're limiting ourselves to 32b subspace for this SAC trick and we fail the alloc, then we can try the space above 32b first (if usable). If that fails, then retry there. I don't see a need to retry the 32b subspace if we're not limited to it. How about it? We tried that idea and it looks to just about restore performance. The thing is, if you do have an actual PCI device where DAC might mean a 33% throughput loss and you're mapping a long-lived buffer, or you're on one of these systems where firmware fails to document address limits and using the full IOMMU address width quietly breaks things, then you almost certainly*do* want the
Re: [PATCH 1/1] Revert "iommu/iova: Retry from last rb tree node if iova search fails"
On 01/03/2021 15:48, John Garry wrote: While max32_alloc_size indirectly tracks the largest*contiguous* available space, one of the ideas from which it grew was to simply keep count of the total number of free PFNs. If you're really spending significant time determining that the tree is full, as opposed to just taking longer to eventually succeed, then it might be relatively innocuous to tack on that semi-redundant extra accounting as a self-contained quick fix for that worst case. Anyway, we see ~50% throughput regression, which is intolerable. As seen in [0], I put this down to the fact that we have so many IOVA requests which exceed the rcache size limit, which means many RB tree accesses for non-cacheble IOVAs, which are now slower. I will attempt to prove this by increasing RCACHE RANGE, such that all IOVA sizes may be cached. About this one, as expected, we restore performance by increasing the RCACHE RANGE. Some figures: Baseline v5.12-rc1 strict mode: 600K IOPs Revert "iommu/iova: Retry from last rb tree node if iova search fails": 1215K Increase IOVA RCACHE range 6 -> 10 (All IOVAs size requests now cacheable for this experiment): 1400K Reduce LLDD max SGE count 124 -> 16: 1288K non-strict mode 1650K So ideally we can work towards something for which IOVAs of all size could be cached. Cheers, John ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH 1/1] Revert "iommu/iova: Retry from last rb tree node if iova search fails"
On 01/03/2021 13:20, Robin Murphy wrote: FWIW, I'm 99% sure that what you really want is [1], but then you get to battle against an unknown quantity of dodgy firmware instead. Something which has not been said before is that this only happens for strict mode. I think that makes sense - once you*have* actually failed to allocate from the 32-bit space, max32_alloc_size will make subsequent attempts fail immediately. In non-strict mode you're most likely freeing 32-bit IOVAs back to the tree - and thus reset max32_alloc_size - much less often, and you'll make more total space available each time, both of which will amortise the cost of getting back into that failed state again. Conversely, the worst case in strict mode is to have multiple threads getting into this pathological cycle: 1: allocate, get last available IOVA 2: allocate, fail and set max32_alloc_size 3: free one IOVA, reset max32_alloc_size, goto 1 Now, given the broken behaviour where the cached PFN can get stuck near the bottom of the address space, step 2 might well have been faster and more premature than it should have, but I hope you can appreciate that relying on an allocator being broken at its fundamental purpose of allocating is not a good or sustainable thing to do. I figure that you're talking about 4e89dce72521 now. I would have liked to know which real-life problem it solved in practice. While max32_alloc_size indirectly tracks the largest*contiguous* available space, one of the ideas from which it grew was to simply keep count of the total number of free PFNs. If you're really spending significant time determining that the tree is full, as opposed to just taking longer to eventually succeed, then it might be relatively innocuous to tack on that semi-redundant extra accounting as a self-contained quick fix for that worst case. Anyway, we see ~50% throughput regression, which is intolerable. As seen in [0], I put this down to the fact that we have so many IOVA requests which exceed the rcache size limit, which means many RB tree accesses for non-cacheble IOVAs, which are now slower. I will attempt to prove this by increasing RCACHE RANGE, such that all IOVA sizes may be cached. On another point, as for longterm IOVA aging issue, it seems that there is no conclusion there. However I did mention the issue of IOVA sizes exceeding rcache size for that issue, so maybe we can find a common solution. Similar to a fixed rcache depot size, it seems that having a fixed rcache max size range value (at 6) doesn't scale either. Well, I'd say that's more of a workload tuning thing than a scalability one - ok a massive system with hundreds of CPUs that spends all day flinging 1500-byte network packets around as fast as it can might be happy with an even smaller value and using the saved memory for something else. IIRC the value of 6 is a fairly arbitrary choice for a tradeoff between expected utility and memory consumption, so making it a Kconfig or command-line tuneable does seem like a sensible thing to explore. Even if it is were configurable, wouldn't it make sense to have it configurable per IOVA domain? Furthermore, as mentioned above, I still want to solve this IOVA aging issue, and this fixed RCACHE RANGE size seems to be the at the center of that problem. As for 4e89dce72521, so even if it's proper to retry for a failed alloc, it is not always necessary. I mean, if we're limiting ourselves to 32b subspace for this SAC trick and we fail the alloc, then we can try the space above 32b first (if usable). If that fails, then retry there. I don't see a need to retry the 32b subspace if we're not limited to it. How about it? We tried that idea and it looks to just about restore performance. The thing is, if you do have an actual PCI device where DAC might mean a 33% throughput loss and you're mapping a long-lived buffer, or you're on one of these systems where firmware fails to document address limits and using the full IOMMU address width quietly breaks things, then you almost certainly*do* want the allocator to actually do a proper job of trying to satisfy the given request. If those conditions were true, then it seems quite a tenuous position, so trying to help that scenario in general terms will have limited efficacy. Furthermore, what you propose is still fragile for your own use-case anyway. If someone makes internal changes to the allocator - converts it to a different tree structure, implements split locking for concurrency, that sort of thing - and it fundamentally loses the dodgy cached32_node behaviour which makes the initial failure unintentionally fast for your workload's allocation pattern, that extra complexity will suddenly just be dead weight and you'll probably be complaining of a performance regression again. We're talking about an allocation that you know you don't need to make, and that you even expect to fail, so I still maintain that it's absurd to focus on optimising
Re: [PATCH 1/1] Revert "iommu/iova: Retry from last rb tree node if iova search fails"
On 2021-02-25 13:54, John Garry wrote: On 29/01/2021 12:03, Robin Murphy wrote: On 2021-01-29 09:48, Leizhen (ThunderTown) wrote: Currently, we are thinking about the solution to the problem. However, because the end time of v5.11 is approaching, this patch is sent first. However, that commit was made for a reason - how do we justify that one thing being slow is more important than another thing being completely broken? It's not practical to just keep doing the patch hokey-cokey based on whoever shouts loudest :( On 2021/1/29 17:21, Zhen Lei wrote: This reverts commit 4e89dce725213d3d0b0475211b500eda4ef4bf2f. We find that this patch has a great impact on performance. According to our test: the iops decreases from 1655.6K to 893.5K, about half. Hardware: 1 SAS expander with 12 SAS SSD Command: Only the main parameters are listed. fio bs=4k rw=read iodepth=128 cpus_allowed=0-127 FWIW, I'm 99% sure that what you really want is [1], but then you get to battle against an unknown quantity of dodgy firmware instead. Something which has not been said before is that this only happens for strict mode. I think that makes sense - once you *have* actually failed to allocate from the 32-bit space, max32_alloc_size will make subsequent attempts fail immediately. In non-strict mode you're most likely freeing 32-bit IOVAs back to the tree - and thus reset max32_alloc_size - much less often, and you'll make more total space available each time, both of which will amortise the cost of getting back into that failed state again. Conversely, the worst case in strict mode is to have multiple threads getting into this pathological cycle: 1: allocate, get last available IOVA 2: allocate, fail and set max32_alloc_size 3: free one IOVA, reset max32_alloc_size, goto 1 Now, given the broken behaviour where the cached PFN can get stuck near the bottom of the address space, step 2 might well have been faster and more premature than it should have, but I hope you can appreciate that relying on an allocator being broken at its fundamental purpose of allocating is not a good or sustainable thing to do. While max32_alloc_size indirectly tracks the largest *contiguous* available space, one of the ideas from which it grew was to simply keep count of the total number of free PFNs. If you're really spending significant time determining that the tree is full, as opposed to just taking longer to eventually succeed, then it might be relatively innocuous to tack on that semi-redundant extra accounting as a self-contained quick fix for that worst case. Anyway, we see ~50% throughput regression, which is intolerable. As seen in [0], I put this down to the fact that we have so many IOVA requests which exceed the rcache size limit, which means many RB tree accesses for non-cacheble IOVAs, which are now slower. On another point, as for longterm IOVA aging issue, it seems that there is no conclusion there. However I did mention the issue of IOVA sizes exceeding rcache size for that issue, so maybe we can find a common solution. Similar to a fixed rcache depot size, it seems that having a fixed rcache max size range value (at 6) doesn't scale either. Well, I'd say that's more of a workload tuning thing than a scalability one - a massive system with hundreds of CPUs that spends all day flinging 1500-byte network packets around as fast as it can might be happy with an even smaller value and using the saved memory for something else. IIRC the value of 6 is a fairly arbitrary choice for a tradeoff between expected utility and memory consumption, so making it a Kconfig or command-line tuneable does seem like a sensible thing to explore. As for 4e89dce72521, so even if it's proper to retry for a failed alloc, it is not always necessary. I mean, if we're limiting ourselves to 32b subspace for this SAC trick and we fail the alloc, then we can try the space above 32b first (if usable). If that fails, then retry there. I don't see a need to retry the 32b subspace if we're not limited to it. How about it? We tried that idea and it looks to just about restore performance. The thing is, if you do have an actual PCI device where DAC might mean a 33% throughput loss and you're mapping a long-lived buffer, or you're on one of these systems where firmware fails to document address limits and using the full IOMMU address width quietly breaks things, then you almost certainly *do* want the allocator to actually do a proper job of trying to satisfy the given request. Furthermore, what you propose is still fragile for your own use-case anyway. If someone makes internal changes to the allocator - converts it to a different tree structure, implements split locking for concurrency, that sort of thing - and it fundamentally loses the dodgy cached32_node behaviour which makes the initial failure unintentionally fast for your workload's allocation pattern, that extra complexity
Re: [PATCH 1/1] Revert "iommu/iova: Retry from last rb tree node if iova search fails"
On 29/01/2021 12:03, Robin Murphy wrote: On 2021-01-29 09:48, Leizhen (ThunderTown) wrote: Currently, we are thinking about the solution to the problem. However, because the end time of v5.11 is approaching, this patch is sent first. However, that commit was made for a reason - how do we justify that one thing being slow is more important than another thing being completely broken? It's not practical to just keep doing the patch hokey-cokey based on whoever shouts loudest :( On 2021/1/29 17:21, Zhen Lei wrote: This reverts commit 4e89dce725213d3d0b0475211b500eda4ef4bf2f. We find that this patch has a great impact on performance. According to our test: the iops decreases from 1655.6K to 893.5K, about half. Hardware: 1 SAS expander with 12 SAS SSD Command: Only the main parameters are listed. fio bs=4k rw=read iodepth=128 cpus_allowed=0-127 FWIW, I'm 99% sure that what you really want is [1], but then you get to battle against an unknown quantity of dodgy firmware instead. Something which has not been said before is that this only happens for strict mode. Anyway, we see ~50% throughput regression, which is intolerable. As seen in [0], I put this down to the fact that we have so many IOVA requests which exceed the rcache size limit, which means many RB tree accesses for non-cacheble IOVAs, which are now slower. On another point, as for longterm IOVA aging issue, it seems that there is no conclusion there. However I did mention the issue of IOVA sizes exceeding rcache size for that issue, so maybe we can find a common solution. Similar to a fixed rcache depot size, it seems that having a fixed rcache max size range value (at 6) doesn't scale either. As for 4e89dce72521, so even if it's proper to retry for a failed alloc, it is not always necessary. I mean, if we're limiting ourselves to 32b subspace for this SAC trick and we fail the alloc, then we can try the space above 32b first (if usable). If that fails, then retry there. I don't see a need to retry the 32b subspace if we're not limited to it. How about it? We tried that idea and it looks to just about restore performance. Thanks, John [0] https://raw.githubusercontent.com/hisilicon/kernel-dev/topic-iommu-5.10-iova-debug-v3/aging_test ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH 1/1] Revert "iommu/iova: Retry from last rb tree node if iova search fails"
Hi Robin,
在 2021/1/29 20:03, Robin Murphy 写道:
On 2021-01-29 09:48, Leizhen (ThunderTown) wrote:
Currently, we are thinking about the solution to the problem.
However, because the end time of v5.11 is approaching, this patch is
sent first.
However, that commit was made for a reason - how do we justify that
one thing being slow is more important than another thing being
completely broken? It's not practical to just keep doing the patch
hokey-cokey based on whoever shouts loudest :(
On 2021/1/29 17:21, Zhen Lei wrote:
This reverts commit 4e89dce725213d3d0b0475211b500eda4ef4bf2f.
We find that this patch has a great impact on performance. According to
our test: the iops decreases from 1655.6K to 893.5K, about half.
Hardware: 1 SAS expander with 12 SAS SSD
Command: Only the main parameters are listed.
fio bs=4k rw=read iodepth=128 cpus_allowed=0-127
FWIW, I'm 99% sure that what you really want is [1], but then you get
to battle against an unknown quantity of dodgy firmware instead.
Robin.
[1]
https://lore.kernel.org/linux-iommu/d412c292d222eb36469effd338e985f9d9e24cd6.1594207679.git.robin.mur...@arm.com/
Thank you for pointing that out. I have tested it, and it solves the
performance drop issue mentioned above.
I noticed that you sent it July 2020, and do you have a plan to merge it
recently?
Fixes: 4e89dce72521 ("iommu/iova: Retry from last rb tree node if
iova search fails")
Tested-by: Xiang Chen
Signed-off-by: Zhen Lei
---
drivers/iommu/iova.c | 23 ++-
1 file changed, 6 insertions(+), 17 deletions(-)
diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index d20b8b333d30d17..f840c7207efbced 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -185,9 +185,8 @@ static int __alloc_and_insert_iova_range(struct
iova_domain *iovad,
struct rb_node *curr, *prev;
struct iova *curr_iova;
unsigned long flags;
-unsigned long new_pfn, retry_pfn;
+unsigned long new_pfn;
unsigned long align_mask = ~0UL;
-unsigned long high_pfn = limit_pfn, low_pfn = iovad->start_pfn;
if (size_aligned)
align_mask <<= fls_long(size - 1);
@@ -200,25 +199,15 @@ static int
__alloc_and_insert_iova_range(struct iova_domain *iovad,
curr = __get_cached_rbnode(iovad, limit_pfn);
curr_iova = rb_entry(curr, struct iova, node);
-retry_pfn = curr_iova->pfn_hi + 1;
-
-retry:
do {
-high_pfn = min(high_pfn, curr_iova->pfn_lo);
-new_pfn = (high_pfn - size) & align_mask;
+limit_pfn = min(limit_pfn, curr_iova->pfn_lo);
+new_pfn = (limit_pfn - size) & align_mask;
prev = curr;
curr = rb_prev(curr);
curr_iova = rb_entry(curr, struct iova, node);
-} while (curr && new_pfn <= curr_iova->pfn_hi && new_pfn >=
low_pfn);
-
-if (high_pfn < size || new_pfn < low_pfn) {
-if (low_pfn == iovad->start_pfn && retry_pfn < limit_pfn) {
-high_pfn = limit_pfn;
-low_pfn = retry_pfn;
-curr = >anchor.node;
-curr_iova = rb_entry(curr, struct iova, node);
-goto retry;
-}
+} while (curr && new_pfn <= curr_iova->pfn_hi);
+
+if (limit_pfn < size || new_pfn < iovad->start_pfn) {
iovad->max32_alloc_size = size;
goto iova32_full;
}
.
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Re: [PATCH 1/1] Revert "iommu/iova: Retry from last rb tree node if iova search fails"
On 2021-01-29 09:48, Leizhen (ThunderTown) wrote:
Currently, we are thinking about the solution to the problem. However, because
the end time of v5.11 is approaching, this patch is sent first.
However, that commit was made for a reason - how do we justify that one
thing being slow is more important than another thing being completely
broken? It's not practical to just keep doing the patch hokey-cokey
based on whoever shouts loudest :(
On 2021/1/29 17:21, Zhen Lei wrote:
This reverts commit 4e89dce725213d3d0b0475211b500eda4ef4bf2f.
We find that this patch has a great impact on performance. According to
our test: the iops decreases from 1655.6K to 893.5K, about half.
Hardware: 1 SAS expander with 12 SAS SSD
Command: Only the main parameters are listed.
fio bs=4k rw=read iodepth=128 cpus_allowed=0-127
FWIW, I'm 99% sure that what you really want is [1], but then you get to
battle against an unknown quantity of dodgy firmware instead.
Robin.
[1]
https://lore.kernel.org/linux-iommu/d412c292d222eb36469effd338e985f9d9e24cd6.1594207679.git.robin.mur...@arm.com/
Fixes: 4e89dce72521 ("iommu/iova: Retry from last rb tree node if iova search
fails")
Tested-by: Xiang Chen
Signed-off-by: Zhen Lei
---
drivers/iommu/iova.c | 23 ++-
1 file changed, 6 insertions(+), 17 deletions(-)
diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index d20b8b333d30d17..f840c7207efbced 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -185,9 +185,8 @@ static int __alloc_and_insert_iova_range(struct iova_domain
*iovad,
struct rb_node *curr, *prev;
struct iova *curr_iova;
unsigned long flags;
- unsigned long new_pfn, retry_pfn;
+ unsigned long new_pfn;
unsigned long align_mask = ~0UL;
- unsigned long high_pfn = limit_pfn, low_pfn = iovad->start_pfn;
if (size_aligned)
align_mask <<= fls_long(size - 1);
@@ -200,25 +199,15 @@ static int __alloc_and_insert_iova_range(struct
iova_domain *iovad,
curr = __get_cached_rbnode(iovad, limit_pfn);
curr_iova = rb_entry(curr, struct iova, node);
- retry_pfn = curr_iova->pfn_hi + 1;
-
-retry:
do {
- high_pfn = min(high_pfn, curr_iova->pfn_lo);
- new_pfn = (high_pfn - size) & align_mask;
+ limit_pfn = min(limit_pfn, curr_iova->pfn_lo);
+ new_pfn = (limit_pfn - size) & align_mask;
prev = curr;
curr = rb_prev(curr);
curr_iova = rb_entry(curr, struct iova, node);
- } while (curr && new_pfn <= curr_iova->pfn_hi && new_pfn >= low_pfn);
-
- if (high_pfn < size || new_pfn < low_pfn) {
- if (low_pfn == iovad->start_pfn && retry_pfn < limit_pfn) {
- high_pfn = limit_pfn;
- low_pfn = retry_pfn;
- curr = >anchor.node;
- curr_iova = rb_entry(curr, struct iova, node);
- goto retry;
- }
+ } while (curr && new_pfn <= curr_iova->pfn_hi);
+
+ if (limit_pfn < size || new_pfn < iovad->start_pfn) {
iovad->max32_alloc_size = size;
goto iova32_full;
}
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Re: [PATCH 1/1] Revert "iommu/iova: Retry from last rb tree node if iova search fails"
Currently, we are thinking about the solution to the problem. However, because
the end time of v5.11 is approaching, this patch is sent first.
On 2021/1/29 17:21, Zhen Lei wrote:
> This reverts commit 4e89dce725213d3d0b0475211b500eda4ef4bf2f.
>
> We find that this patch has a great impact on performance. According to
> our test: the iops decreases from 1655.6K to 893.5K, about half.
>
> Hardware: 1 SAS expander with 12 SAS SSD
> Command: Only the main parameters are listed.
> fio bs=4k rw=read iodepth=128 cpus_allowed=0-127
>
> Fixes: 4e89dce72521 ("iommu/iova: Retry from last rb tree node if iova search
> fails")
> Tested-by: Xiang Chen
> Signed-off-by: Zhen Lei
> ---
> drivers/iommu/iova.c | 23 ++-
> 1 file changed, 6 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index d20b8b333d30d17..f840c7207efbced 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -185,9 +185,8 @@ static int __alloc_and_insert_iova_range(struct
> iova_domain *iovad,
> struct rb_node *curr, *prev;
> struct iova *curr_iova;
> unsigned long flags;
> - unsigned long new_pfn, retry_pfn;
> + unsigned long new_pfn;
> unsigned long align_mask = ~0UL;
> - unsigned long high_pfn = limit_pfn, low_pfn = iovad->start_pfn;
>
> if (size_aligned)
> align_mask <<= fls_long(size - 1);
> @@ -200,25 +199,15 @@ static int __alloc_and_insert_iova_range(struct
> iova_domain *iovad,
>
> curr = __get_cached_rbnode(iovad, limit_pfn);
> curr_iova = rb_entry(curr, struct iova, node);
> - retry_pfn = curr_iova->pfn_hi + 1;
> -
> -retry:
> do {
> - high_pfn = min(high_pfn, curr_iova->pfn_lo);
> - new_pfn = (high_pfn - size) & align_mask;
> + limit_pfn = min(limit_pfn, curr_iova->pfn_lo);
> + new_pfn = (limit_pfn - size) & align_mask;
> prev = curr;
> curr = rb_prev(curr);
> curr_iova = rb_entry(curr, struct iova, node);
> - } while (curr && new_pfn <= curr_iova->pfn_hi && new_pfn >= low_pfn);
> -
> - if (high_pfn < size || new_pfn < low_pfn) {
> - if (low_pfn == iovad->start_pfn && retry_pfn < limit_pfn) {
> - high_pfn = limit_pfn;
> - low_pfn = retry_pfn;
> - curr = >anchor.node;
> - curr_iova = rb_entry(curr, struct iova, node);
> - goto retry;
> - }
> + } while (curr && new_pfn <= curr_iova->pfn_hi);
> +
> + if (limit_pfn < size || new_pfn < iovad->start_pfn) {
> iovad->max32_alloc_size = size;
> goto iova32_full;
> }
>
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[PATCH 1/1] Revert "iommu/iova: Retry from last rb tree node if iova search fails"
This reverts commit 4e89dce725213d3d0b0475211b500eda4ef4bf2f.
We find that this patch has a great impact on performance. According to
our test: the iops decreases from 1655.6K to 893.5K, about half.
Hardware: 1 SAS expander with 12 SAS SSD
Command: Only the main parameters are listed.
fio bs=4k rw=read iodepth=128 cpus_allowed=0-127
Fixes: 4e89dce72521 ("iommu/iova: Retry from last rb tree node if iova search
fails")
Tested-by: Xiang Chen
Signed-off-by: Zhen Lei
---
drivers/iommu/iova.c | 23 ++-
1 file changed, 6 insertions(+), 17 deletions(-)
diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index d20b8b333d30d17..f840c7207efbced 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -185,9 +185,8 @@ static int __alloc_and_insert_iova_range(struct iova_domain
*iovad,
struct rb_node *curr, *prev;
struct iova *curr_iova;
unsigned long flags;
- unsigned long new_pfn, retry_pfn;
+ unsigned long new_pfn;
unsigned long align_mask = ~0UL;
- unsigned long high_pfn = limit_pfn, low_pfn = iovad->start_pfn;
if (size_aligned)
align_mask <<= fls_long(size - 1);
@@ -200,25 +199,15 @@ static int __alloc_and_insert_iova_range(struct
iova_domain *iovad,
curr = __get_cached_rbnode(iovad, limit_pfn);
curr_iova = rb_entry(curr, struct iova, node);
- retry_pfn = curr_iova->pfn_hi + 1;
-
-retry:
do {
- high_pfn = min(high_pfn, curr_iova->pfn_lo);
- new_pfn = (high_pfn - size) & align_mask;
+ limit_pfn = min(limit_pfn, curr_iova->pfn_lo);
+ new_pfn = (limit_pfn - size) & align_mask;
prev = curr;
curr = rb_prev(curr);
curr_iova = rb_entry(curr, struct iova, node);
- } while (curr && new_pfn <= curr_iova->pfn_hi && new_pfn >= low_pfn);
-
- if (high_pfn < size || new_pfn < low_pfn) {
- if (low_pfn == iovad->start_pfn && retry_pfn < limit_pfn) {
- high_pfn = limit_pfn;
- low_pfn = retry_pfn;
- curr = >anchor.node;
- curr_iova = rb_entry(curr, struct iova, node);
- goto retry;
- }
+ } while (curr && new_pfn <= curr_iova->pfn_hi);
+
+ if (limit_pfn < size || new_pfn < iovad->start_pfn) {
iovad->max32_alloc_size = size;
goto iova32_full;
}
--
1.8.3
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