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Date:   Mon, 23 Sep 2019 10:35:49 +0200
From:   Ingo Molnar <mingo@kernel.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     "Pavel Begunkov (Silence)" <asml.silence@gmail.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/2] Optimise io_uring completion waiting
Message-ID: <20190923083549.GA42487@gmail.com>
References: <cover.1569139018.git.asml.silence@gmail.com>
 <a4996ae7-ac0a-447b-49b2-7e96275aad29@kernel.dk>
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* Jens Axboe <axboe@kernel.dk> wrote:

> On 9/22/19 2:08 AM, Pavel Begunkov (Silence) wrote:
> > From: Pavel Begunkov <asml.silence@gmail.com>
> > 
> > There could be a lot of overhead within generic wait_event_*() used for
> > waiting for large number of completions. The patchset removes much of
> > it by using custom wait event (wait_threshold).
> > 
> > Synthetic test showed ~40% performance boost. (see patch 2)
> 
> I'm fine with the io_uring side of things, but to queue this up we
> really need Peter or Ingo to sign off on the core wakeup bits...
> 
> Peter?

I'm not sure an extension is needed for such a special interface, why not 
just put a ->threshold value next to the ctx->wait field and use either 
the regular wait_event() APIs with the proper condition, or 
wait_event_cmd() style APIs if you absolutely need something more complex 
to happen inside?

Should result in a much lower linecount and no scheduler changes. :-)

Thanks,

	Ingo