Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] io_uring: reduce latency by reissueing the operation
To:     Olivier Langlois <olivier@trillion01.com>,
        Pavel Begunkov <asml.silence@gmail.com>,
        io-uring@vger.kernel.org, linux-kernel@vger.kernel.org
References: <60c13bec.1c69fb81.f2c1e.6444SMTPIN_ADDED_MISSING@mx.google.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <ff0aab90-9aef-4ec6-f00f-89d4ffa21ef6@kernel.dk>
Date:   Wed, 16 Jun 2021 06:48:52 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <60c13bec.1c69fb81.f2c1e.6444SMTPIN_ADDED_MISSING@mx.google.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 6/9/21 4:08 PM, Olivier Langlois wrote:
> It is quite frequent that when an operation fails and returns EAGAIN,
> the data becomes available between that failure and the call to
> vfs_poll() done by io_arm_poll_handler().
> 
> Detecting the situation and reissuing the operation is much faster
> than going ahead and push the operation to the io-wq.

I think this is obviously the right thing to do, but I'm not too crazy
about the 'ret' pointer passed in. We could either add a proper return
type instead of the bool and use that, or put the poll-or-queue-async
into a helper that then only needs a bool return, and use that return
value for whether to re-issue or not.

Care to send an updated variant?

-- 
Jens Axboe