Re: [PATCH 1/1] Revert "iommu/iova: Retry from last rb tree node if iova search fails"

Fri, 29 Jan 2021 04:44:58 -0800 

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 <[email protected]>
Signed-off-by: Zhen Lei <[email protected]>
---
  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 = &iovad->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;
      }





.




_______________________________________________
iommu mailing list
[email protected]
https://lists.linuxfoundation.org/mailman/listinfo/iommu

Reply via email to