linux-kernel - Re: [PATCH RFC v2 3/3] io_uring: batch get(ctx->ref) across submits

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Message-ID: <ff85b807-83e1-fd05-5f85-dcf465a50c11@kernel.dk>
Date:   Sat, 21 Dec 2019 09:38:28 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Tejun Heo <tj@...nel.org>, Dennis Zhou <dennis@...nel.org>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH RFC v2 3/3] io_uring: batch get(ctx->ref) across submits

On 12/21/19 9:20 AM, Pavel Begunkov wrote:
> On 21/12/2019 19:15, Pavel Begunkov wrote:
>> Double account ctx->refs keeping number of taken refs in ctx. As
>> io_uring gets per-request ctx->refs during submission, while holding
>> ctx->uring_lock, this allows in most of the time to bypass
>> percpu_ref_get*() and its overhead.
> 
> Jens, could you please benchmark with this one? Especially for offloaded QD1
> case. I haven't got any difference for nops test and don't have a decent SSD
> at hands to test it myself. We could drop it, if there is no benefit.
> 
> This rewrites that @extra_refs from the second one, so I left it for now.

Sure, let me run a peak test, qd1 test, qd1+sqpoll test on
for-5.6/io_uring, same branch with 1-2, and same branch with 1-3. That
should give us a good comparison. One core used for all, and we're going
to be core speed bound for the performance in all cases on this setup.
So it'll be a good comparison.

-- 
Jens Axboe