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From: Jens Axboe <>
To: "Pavel Begunkov" <>,
	io-uring <>, 李通洲 <>
Subject: Re: [RFC] single cqe per link
Date: Mon, 24 Feb 2020 19:24:09 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 2/24/20 5:39 PM, Pavel Begunkov wrote:
> I've got curious about performance of the idea of having only 1 CQE per link
> (for the failed or last one). Tested it with a quick dirty patch doing
> submit-and-reap of a nops-link (patched for inline execution).
> 1) link size: 100
> old: 206 ns per nop
> new: 144 ns per nop
> 2) link size: 10
> old: 234 ns per nop
> new: 181 ns per nop
> 3) link size: 10, FORCE_ASYNC
> old: 667 ns per nop
> new: 569 ns per nop
> The patch below breaks sequences, linked_timeout and who knows what else.
> The first one requires synchronisation/atomic, so it's a bit in the way. I've
> been wondering, whether IOSQE_IO_DRAIN is popular and how much it's used. We can
> try to find tradeoff or even disable it with this feature.

For a more realistic workload, I can try and run a random read workload
on a fast device. If I just make the QD the link count, then we'll
have the same amount in parallel, just with link-depth ratio less
CQEs. I'd be curious to see what that does.

Jens Axboe

      parent reply	other threads:[~2020-02-25  2:24 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-25  0:39 [RFC] single cqe per link Pavel Begunkov
2020-02-25  2:14 ` Carter Li 李通洲
2020-02-25  2:36   ` Jens Axboe
2020-02-25  3:13     ` Jens Axboe
2020-02-25 10:12       ` Pavel Begunkov
2020-02-25 20:20         ` Jens Axboe
2020-02-25 21:13           ` Pavel Begunkov
2020-08-21  5:17             ` Questions about IORING_OP_ASYNC_CANCEL usage Carter Li 李通洲
2020-08-21  5:20               ` Carter Li 李通洲
2020-02-25  2:24 ` Jens Axboe [this message]

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