Re: [PATCH v4 00/23] backup performance: block_status + async

[Max Reitz <mreitz@redhat.com>]

On 20.01.21 11:39, Max Reitz wrote:
> On 19.01.21 20:22, Vladimir Sementsov-Ogievskiy wrote:
>> 19.01.2021 21:40, Max Reitz wrote:
>>> On 16.01.21 22:46, Vladimir Sementsov-Ogievskiy wrote:
>>>> Hi Max!
>>>> I applied my series onto yours 129-fixing and found, that 129 fails 
>>>> for backup.
>>>> And setting small max-chunk and even max-workers to 1 doesn't help! 
>>>> (setting
>>>> speed like in v3 still helps).
>>>>
>>>> And I found, that the problem is that really, the whole backup job 
>>>> goes during
>>>> drain, because in new architecture we do just job_yield() during the 
>>>> whole
>>>> background block-copy.
>>>>
>>>> This leads to modifying the existing patch in the series, which does 
>>>> job_enter()
>>>> from job_user_pause: we just need call job_enter() from job_pause() 
>>>> to cover
>>>> not only user pauses but also drained_begin.
>>>>
>>>> So, now I don't need any additional fixing of 129.
>>>>
>>>> Changes in v4:
>>>> - add a lot of Max's r-b's, thanks!
>>>>
>>>> 03: fix over-80 line (in comment), add r-b
>>>> 09: was "[PATCH v3 10/25] job: call job_enter from job_user_pause",
>>>>      now changed to finally fix 129 iotest, drop r-b
>>>>
>>>> 10: squash-in additional wording on max-chunk, fix error message, 
>>>> keep r-b
>>>> 17: drop extra include, assert job_is_cancelled() instead of check, 
>>>> add r-b
>>>> 18: adjust commit message, add r-b
>>>> 23: add comments and assertion, about the fact that test doesn't 
>>>> support
>>>>      paths with colon inside
>>>>      fix s/disable-copy-range/use-copy-range/
>>>
>>> Hmmm, for me, 129 sometimes fails still, because it completes too 
>>> quickly...  (The error then is that 'return[0]' does not exist in 
>>> query-block-jobs’s result, because the job is already gone.)
>>>
>>> When I insert a print(result) after the query-block-jobs, I can see 
>>> that the job has always progressed really far, even if its still 
>>> running. (Like, generally the offset is just one MB shy of 1G.)
>>>
>>> I suspect the problem is that block-copy just copies too much from 
>>> the start (by default); i.e., it starts 64 workers with, hm, well, 1 
>>> MB of chunk size?  Shouldn’t fill the 128 MB immediately...
>>>
>>> Anyway, limiting the number of workers (to 1) and the chunk size (to 
>>> 64k) with x-perf does ensure that the backup job’s progress is 
>>> limited to 1 MB or so, which looks fine to me.
>>>
>>> I suppose we should do that, then (in 129), before patch 17?
>>
>> Yes, that sounds reasonable
>>
>>>
>>> (PS: I can also see a MacOS failure in iotest 256.  I suspect it’s 
>>> related to this series, because 256 is a backup test (with 
>>> iothreads), but I’m not sure yet.  The log is here:
>>>
>>> https://cirrus-ci.com/task/5276331753603072
>>> )
>>>
>>
>> qemu received signal 31 ?
>>
>> googling for MacOS...
>>
>>   31    SIGUSR2      terminate process    User defined signal 2
> 
> coroutine-sigaltstack uses SIGUSR2 to set up new coroutines.  Perhaps 
> it’s unrelated to backup?  Guess I’ll just run the test one more time. O:)

I ran it again, got the same error.  There is no error on master, or 
before backup uses block_copy.

I’m trying to run a test directly on the “move to block-copy” commit, 
but so far Cirrus doesn’t seem to want me to do another test run right now.

(Though I’m pretty sure if there is no error before the block-copy 
commit, then using block-copy must be the problem.  The remaining 
patches in my block branch are just disabling copy_range, some clean-up, 
the simplebench patches, the locking code error reporting change, and a 
new iotest.)

Max