Re: [Qemu-devel] [PULL 02/17] cpu_physical_memory_sync_dirty_bitmap: Fix alignment check

[Alex Bennée]

Dr. David Alan Gilbert  writes:

> * Peter Maydell (peter.mayd...@linaro.org) wrote:
>> On 1 August 2017 at 17:17, Paolo Bonzini  wrote:
>> > From: "Dr. David Alan Gilbert" 
>> >
>> > This code has an optimised, word aligned version, and a boring
>> > unaligned version.  Recently 084140bd498909 fixed a missing offset
>> > addition from the core of both versions.  However, the offset isn't
>> > necessarily aligned and thus the choice between the two versions
>> > needs fixing up to also include the offset.
>> >
>> > Symptom:
>> >   A few stuck unsent pages during migration; not normally noticed
>> > unless under very low bandwidth in which case the migration may get
>> > stuck never ending and never performing a 2nd sync; noticed by
>> > a hanging postcopy-test on a very heavily loaded system.
>> >
>> > Fixes: 084140bd498909
>> >
>> > Signed-off-by: Dr. David Alan Gilbert 
>> > Reported-by: Alex Benneé 
>> > Tested-by: Alex Benneé 
>> >
>> > --
>> > v2
>> >   Move 'page' inside the if (Comment from Paolo)
>> > Message-Id: <20170724165125.29887-1-dgilb...@redhat.com>
>> > Signed-off-by: Paolo Bonzini 
>>
>> Something somewhere along the line seems to have mangled the
>> unicode characters in Alex's name :-(
>> Also, Alex's email address is typoed, and what should be the
>> '---' marker has been written as '--' so the below-the-fold waffle
>> is still hanging around in the commit.
>>
>> This doesn't seem worth rejecting the pull request on the
>> eve of rc1 for, but it's still a bit sad :-(
>
> Hmm yes, I think some of that's mine - the missing 'n' is certainly
> my fault; and I may have got his two 'e's in the wrong order,
> but I don't know what changed the encoding, that seems right on:
>   https://lists.nongnu.org/archive/html/qemu-devel/2017-07/msg07417.html

Hmm also the acute accent should be on the second (not third) e ;-)

--
Alex Bennée
(breaking UTF-8 workflow since before it was cool)

Re: [Qemu-devel] [PULL 02/17] cpu_physical_memory_sync_dirty_bitmap: Fix alignment check

[Paolo Bonzini]

On 01/08/2017 20:04, Dr. David Alan Gilbert wrote:
> * Peter Maydell (peter.mayd...@linaro.org) wrote:
>> On 1 August 2017 at 17:17, Paolo Bonzini  wrote:
>>> From: "Dr. David Alan Gilbert" 
>>>
>>> This code has an optimised, word aligned version, and a boring
>>> unaligned version.  Recently 084140bd498909 fixed a missing offset
>>> addition from the core of both versions.  However, the offset isn't
>>> necessarily aligned and thus the choice between the two versions
>>> needs fixing up to also include the offset.
>>>
>>> Symptom:
>>>   A few stuck unsent pages during migration; not normally noticed
>>> unless under very low bandwidth in which case the migration may get
>>> stuck never ending and never performing a 2nd sync; noticed by
>>> a hanging postcopy-test on a very heavily loaded system.
>>>
>>> Fixes: 084140bd498909
>>>
>>> Signed-off-by: Dr. David Alan Gilbert 
>>> Reported-by: Alex Benneé 
>>> Tested-by: Alex Benneé 
>>>
>>> --
>>> v2
>>>   Move 'page' inside the if (Comment from Paolo)
>>> Message-Id: <20170724165125.29887-1-dgilb...@redhat.com>
>>> Signed-off-by: Paolo Bonzini 
>>
>> Something somewhere along the line seems to have mangled the
>> unicode characters in Alex's name :-(
>> Also, Alex's email address is typoed, and what should be the
>> '---' marker has been written as '--' so the below-the-fold waffle
>> is still hanging around in the commit.
>>
>> This doesn't seem worth rejecting the pull request on the
>> eve of rc1 for, but it's still a bit sad :-(
> 
> Hmm yes, I think some of that's mine - the missing 'n' is certainly
> my fault; and I may have got his two 'e's in the wrong order,
> but I don't know what changed the encoding, that seems right on:
>   https://lists.nongnu.org/archive/html/qemu-devel/2017-07/msg07417.html

The encoding is me.

Paolo

Re: [Qemu-devel] [PULL 02/17] cpu_physical_memory_sync_dirty_bitmap: Fix alignment check

[Dr. David Alan Gilbert]

* Peter Maydell (peter.mayd...@linaro.org) wrote:
> On 1 August 2017 at 17:17, Paolo Bonzini  wrote:
> > From: "Dr. David Alan Gilbert" 
> >
> > This code has an optimised, word aligned version, and a boring
> > unaligned version.  Recently 084140bd498909 fixed a missing offset
> > addition from the core of both versions.  However, the offset isn't
> > necessarily aligned and thus the choice between the two versions
> > needs fixing up to also include the offset.
> >
> > Symptom:
> >   A few stuck unsent pages during migration; not normally noticed
> > unless under very low bandwidth in which case the migration may get
> > stuck never ending and never performing a 2nd sync; noticed by
> > a hanging postcopy-test on a very heavily loaded system.
> >
> > Fixes: 084140bd498909
> >
> > Signed-off-by: Dr. David Alan Gilbert 
> > Reported-by: Alex Benneé 
> > Tested-by: Alex Benneé 
> >
> > --
> > v2
> >   Move 'page' inside the if (Comment from Paolo)
> > Message-Id: <20170724165125.29887-1-dgilb...@redhat.com>
> > Signed-off-by: Paolo Bonzini 
> 
> Something somewhere along the line seems to have mangled the
> unicode characters in Alex's name :-(
> Also, Alex's email address is typoed, and what should be the
> '---' marker has been written as '--' so the below-the-fold waffle
> is still hanging around in the commit.
> 
> This doesn't seem worth rejecting the pull request on the
> eve of rc1 for, but it's still a bit sad :-(

Hmm yes, I think some of that's mine - the missing 'n' is certainly
my fault; and I may have got his two 'e's in the wrong order,
but I don't know what changed the encoding, that seems right on:
  https://lists.nongnu.org/archive/html/qemu-devel/2017-07/msg07417.html

Dave

> thanks
> -- PMM
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK

Re: [Qemu-devel] [PULL 02/17] cpu_physical_memory_sync_dirty_bitmap: Fix alignment check

[Peter Maydell]

On 1 August 2017 at 17:17, Paolo Bonzini  wrote:
> From: "Dr. David Alan Gilbert" 
>
> This code has an optimised, word aligned version, and a boring
> unaligned version.  Recently 084140bd498909 fixed a missing offset
> addition from the core of both versions.  However, the offset isn't
> necessarily aligned and thus the choice between the two versions
> needs fixing up to also include the offset.
>
> Symptom:
>   A few stuck unsent pages during migration; not normally noticed
> unless under very low bandwidth in which case the migration may get
> stuck never ending and never performing a 2nd sync; noticed by
> a hanging postcopy-test on a very heavily loaded system.
>
> Fixes: 084140bd498909
>
> Signed-off-by: Dr. David Alan Gilbert 
> Reported-by: Alex Benneé 
> Tested-by: Alex Benneé 
>
> --
> v2
>   Move 'page' inside the if (Comment from Paolo)
> Message-Id: <20170724165125.29887-1-dgilb...@redhat.com>
> Signed-off-by: Paolo Bonzini 

Something somewhere along the line seems to have mangled the
unicode characters in Alex's name :-(
Also, Alex's email address is typoed, and what should be the
'---' marker has been written as '--' so the below-the-fold waffle
is still hanging around in the commit.

This doesn't seem worth rejecting the pull request on the
eve of rc1 for, but it's still a bit sad :-(

thanks
-- PMM

[Qemu-devel] [PULL 02/17] cpu_physical_memory_sync_dirty_bitmap: Fix alignment check

[Paolo Bonzini]

From: "Dr. David Alan Gilbert" 

This code has an optimised, word aligned version, and a boring
unaligned version.  Recently 084140bd498909 fixed a missing offset
addition from the core of both versions.  However, the offset isn't
necessarily aligned and thus the choice between the two versions
needs fixing up to also include the offset.

Symptom:
  A few stuck unsent pages during migration; not normally noticed
unless under very low bandwidth in which case the migration may get
stuck never ending and never performing a 2nd sync; noticed by
a hanging postcopy-test on a very heavily loaded system.

Fixes: 084140bd498909

Signed-off-by: Dr. David Alan Gilbert 
Reported-by: Alex Benneé 
Tested-by: Alex Benneé 

--
v2
  Move 'page' inside the if (Comment from Paolo)
Message-Id: <20170724165125.29887-1-dgilb...@redhat.com>
Signed-off-by: Paolo Bonzini 
---
 include/exec/ram_addr.h | 7 ---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index c04f4f6..d017639 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -377,19 +377,20 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock 
*rb,
uint64_t *real_dirty_pages)
 {
 ram_addr_t addr;
-unsigned long page = BIT_WORD(start >> TARGET_PAGE_BITS);
+unsigned long word = BIT_WORD((start + rb->offset) >> TARGET_PAGE_BITS);
 uint64_t num_dirty = 0;
 unsigned long *dest = rb->bmap;
 
 /* start address is aligned at the start of a word? */
-if (((page * BITS_PER_LONG) << TARGET_PAGE_BITS) == start) {
+if (((word * BITS_PER_LONG) << TARGET_PAGE_BITS) ==
+ (start + rb->offset)) {
 int k;
 int nr = BITS_TO_LONGS(length >> TARGET_PAGE_BITS);
 unsigned long * const *src;
-unsigned long word = BIT_WORD((start + rb->offset) >> 
TARGET_PAGE_BITS);
 unsigned long idx = (word * BITS_PER_LONG) / DIRTY_MEMORY_BLOCK_SIZE;
 unsigned long offset = BIT_WORD((word * BITS_PER_LONG) %
 DIRTY_MEMORY_BLOCK_SIZE);
+unsigned long page = BIT_WORD(start >> TARGET_PAGE_BITS);
 
 rcu_read_lock();
 
-- 
1.8.3.1