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Re: [PATCH 0/3] aio-posix: keep aio_notify_me disabled during polling

From: Paolo Bonzini
Subject: Re: [PATCH 0/3] aio-posix: keep aio_notify_me disabled during polling
Date: Tue, 4 Aug 2020 09:13:17 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0

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


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