From: Olivier Langlois <[email protected]>
To: David Laight <[email protected]>,
'Jens Axboe' <[email protected]>,
Pavel Begunkov <[email protected]>,
"[email protected]" <[email protected]>,
"[email protected]" <[email protected]>
Subject: Re: [PATCH v4] io_uring: reduce latency by reissueing the operation
Date: Mon, 28 Jun 2021 02:42:59 -0400 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On Fri, 2021-06-25 at 08:15 +0000, David Laight wrote:
> From: Jens Axboe
> > Sent: 25 June 2021 01:45
> >
> > On 6/22/21 6:17 AM, 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.
> > >
> > > Performance improvement testing has been performed with:
> > > Single thread, 1 TCP connection receiving a 5 Mbps stream, no
> > > sqpoll.
> > >
> > > 4 measurements have been taken:
> > > 1. The time it takes to process a read request when data is
> > > already available
> > > 2. The time it takes to process by calling twice io_issue_sqe()
> > > after vfs_poll() indicated that data
> > was available
> > > 3. The time it takes to execute io_queue_async_work()
> > > 4. The time it takes to complete a read request asynchronously
> > >
> > > 2.25% of all the read operations did use the new path.
>
> How much slower is it when the data to complete the read isn't
> available?
>
> I suspect there are different workflows where that is almost
> always true.
>
David,
in the case that the data to complete isn't available, the request will
be processed exactly as it was before the patch.
Ideally through io_uring fast polling feature. If not possible because
arming the poll has been aborted, the request will be punted to the io-
wq.
Greetings,
prev parent reply other threads:[~2021-06-28 6:43 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-22 12:17 [PATCH v4] io_uring: reduce latency by reissueing the operation Olivier Langlois
2021-06-22 17:54 ` Pavel Begunkov
2021-06-22 18:01 ` Pavel Begunkov
2021-06-22 19:05 ` Olivier Langlois
2021-06-22 20:51 ` Pavel Begunkov
2021-06-22 20:52 ` Pavel Begunkov
2021-06-25 0:45 ` Jens Axboe
2021-06-25 8:15 ` David Laight
2021-06-28 6:42 ` Olivier Langlois [this message]
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