Re: Fio regression caused by f9fc8932b11f3bcf2a2626f567cb6fdd36a33a94

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, May 05, 2022 at 11:09:08AM +0100, Stefan Hajnoczi wrote:
> On Tue, May 03, 2022 at 09:43:15AM +0200, Lukáš Doktor wrote:
> > Hello Mike, Paolo, others,
> > 
> > in my perf pipeline I noticed a regression bisected to the f9fc8932b11f3bcf2a2626f567cb6fdd36a33a94 - "thread-posix: remove the posix semaphore support" commit and I'd like to ask you to verify it might have caused that and eventually consider fixing it. The regression is visible, reproducible and clearly bisectable to this commit with the following 2 scenarios:
> 
> I can't parse the commit message for
> f9fc8932b11f3bcf2a2626f567cb6fdd36a33a94, so it's not 100% clear to me
> why it was necessary to remove sem_*() calls.
> 
> util/thread-pool.c uses qemu_sem_*() to notify worker threads when work
> becomes available. It makes sense that this operation is
> performance-critical and that's why the benchmark regressed.

Doh, I questioned whether the change would have a performance impact,
and it wasn't thought to be used in perf critical places

   https://www.mail-archive.com/qemu-devel@nongnu.org/msg870737.html

With regards,
Daniel
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