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From: Jens Axboe <[email protected]>
To: Olivier Langlois <[email protected]>,
	Pavel Begunkov <[email protected]>,
	[email protected], [email protected]
Subject: Re: [PATCH v4] io_uring: reduce latency by reissueing the operation
Date: Thu, 24 Jun 2021 18:45:21 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <9e8441419bb1b8f3c3fcc607b2713efecdef2136.1624364038.git.olivier@trillion01.com>

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.
> 
> ready data (baseline)
> avg	3657.94182918628
> min	580
> max	20098
> stddev	1213.15975908162
> 
> reissue	completion
> average	7882.67567567568
> min	2316
> max	28811
> stddev	1982.79172973284
> 
> insert io-wq time
> average	8983.82276995305
> min	3324
> max	87816
> stddev	2551.60056552038
> 
> async time completion
> average	24670.4758861127
> min	10758
> max	102612
> stddev	3483.92416873804
> 
> Conclusion:
> On average reissuing the sqe with the patch code is 1.1uSec faster and
> in the worse case scenario 59uSec faster than placing the request on
> io-wq
> 
> On average completion time by reissuing the sqe with the patch code is
> 16.79uSec faster and in the worse case scenario 73.8uSec faster than
> async completion.

Thanks for respinning with a (much) better commit message. Applied.

-- 
Jens Axboe


  parent reply	other threads:[~2021-06-25  0:45 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 [this message]
2021-06-25  8:15   ` David Laight
2021-06-28  6:42     ` Olivier Langlois

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