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From: Olivier Langlois <[email protected]>
To: Pavel Begunkov <[email protected]>,
	Jens Axboe <[email protected]>,
	[email protected], [email protected]
Subject: Re: [PATCH 1/2 v2] io_uring: Fix race condition when sqp thread goes to sleep
Date: Wed, 23 Jun 2021 09:52:53 -0400	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On Wed, 2021-06-23 at 00:03 +0100, Pavel Begunkov wrote:
> On 6/22/21 11:42 PM, Olivier Langlois wrote:
> > On Tue, 2021-06-22 at 18:37 -0400, Olivier Langlois wrote:
> > > On Tue, 2021-06-22 at 21:45 +0100, Pavel Begunkov wrote:
> > > 
> > > 
> > > I can do that if you want but considering that the function is
> > > inline
> > > and the race condition is a relatively rare occurence, is the
> > > cost
> > > coming with inline expansion really worth it in this case?
> > > > 
> > On hand, there is the inline expansion concern.
> > 
> > OTOH, the benefit of going with your suggestion is that completions
> > generally precedes new submissions so yes, it might be better that
> > way.
> > 
> > I'm really unsure about this. I'm just raising the concern and I'll
> > let
> > you make the final decision...
> 
> It seems it may actually loop infinitely until it gets a signal,
> so yes. And even if not, rare stalls are nasty, they will ruin
> some 9s of latency and hard to catch.
> 
> That part is quite cold anyway, would generate some extra cold
> instructions, meh
> 
I'm not 100% sure to see the infinite loop possibility but I guess that
with some badly placed preemptions, it could take few iterations before
entering the block:

		if (sqt_spin || !time_after(jiffies, timeout)) {

So I will go ahead with your suggestion.

I'll retest the new patch version (it should be a formality) and I'll
resend an update once done.

Greetings,



  reply	other threads:[~2021-06-23 13:52 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-22 18:45 [PATCH 0/2] Minor SQPOLL thread fix and improvement Olivier Langlois, Olivier Langlois
2021-06-22 18:45 ` [PATCH 1/2] io_uring: Fix race condition when sqp thread goes to sleep Olivier Langlois
2021-06-22 18:53   ` Olivier Langlois
2021-06-22 18:55     ` Pavel Begunkov
2021-06-22 19:07       ` Olivier Langlois
     [not found]   ` <[email protected]>
2021-06-22 20:45     ` [PATCH 1/2 v2] " Pavel Begunkov
2021-06-22 22:37       ` Olivier Langlois
2021-06-22 22:42         ` Olivier Langlois
2021-06-22 23:03           ` Pavel Begunkov
2021-06-23 13:52             ` Olivier Langlois [this message]
2021-06-23 15:58               ` Pavel Begunkov
2021-06-22 18:45 ` [PATCH 2/2] io_uring: Create define to modify a SQPOLL parameter Olivier Langlois
2021-06-22 20:58   ` Pavel Begunkov

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