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

[Max Reitz]

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?

(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
)

Max