From: Paolo Bonzini <pbonzini@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>, qemu-devel@nongnu.org
Cc: Fam Zheng <fam@euphon.net>, qemu-block@nongnu.org
Subject: Re: [PATCH 0/3] aio-posix: keep aio_notify_me disabled during polling
Date: Tue, 4 Aug 2020 09:13:17 +0200 [thread overview]
Message-ID: <31b75005-ff3c-70d0-2ffa-a645f74e5082@redhat.com> (raw)
In-Reply-To: <20200804052804.1165291-1-stefanha@redhat.com>
On 04/08/20 07:28, Stefan Hajnoczi wrote:
> This patch series eliminates ctx->notifier EventNotifier activity when
> aio_poll() is in polling mode. There is no need to use the EventNotifier since
> a polling handler can detect that aio_notify() has been called by monitoring a
> field in memory instead.
>
> Optimizing out the EventNotifier calls improves null-co random read 4KB
> iodepth=1 IOPS by 18%.
>
> aio_compute_timeout() is now called twice if aio_poll() needs to block, which
> means an extra qemu_clock_get_ns() call is made when there is an active timer.
> An alternative would be to set timeout = 0 if ctx->notified is true before
> blocking, but going around the event loop again could slow things down more.
>
> I have not modified docs/spin/aio_notify*.promela because I'm not familiar with
> the SPIN model checker.
I'll take a look. Looks good apart from more comments, on which I
commented.
Paolo
prev parent reply other threads:[~2020-08-04 7:14 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-04 5:28 [PATCH 0/3] aio-posix: keep aio_notify_me disabled during polling Stefan Hajnoczi
2020-08-04 5:28 ` [PATCH 1/3] async: rename event_notifier_dummy_cb/poll() Stefan Hajnoczi
2020-08-04 5:28 ` [PATCH 2/3] async: always set ctx->notified in aio_notify() Stefan Hajnoczi
2020-08-04 7:12 ` Paolo Bonzini
2020-08-04 10:23 ` Stefan Hajnoczi
2020-08-04 5:28 ` [PATCH 3/3] aio-posix: keep aio_notify_me disabled during polling Stefan Hajnoczi
2020-08-04 10:29 ` Stefan Hajnoczi
2020-08-04 16:53 ` Paolo Bonzini
2020-08-05 8:59 ` Stefan Hajnoczi
2020-08-04 7:13 ` Paolo Bonzini [this message]
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