linux-kernel - Re: [RFC 00/11] optimise registered buffer/file updates

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Message-ID: <f0dfaa17-fc0e-459e-41ea-8131d558fddb@gmail.com>
Date:   Fri, 31 Mar 2023 17:21:48 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Gabriel Krisman Bertazi <krisman@...e.de>
Cc:     io-uring@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 00/11] optimise registered buffer/file updates

On 3/31/23 14:35, Gabriel Krisman Bertazi wrote:
> Pavel,
> 
> Pavel Begunkov <asml.silence@...il.com> writes:
>> Updating registered files and buffers is a very slow operation, which
>> makes it not feasible for workloads with medium update frequencies.
>> Rework the underlying rsrc infra for greater performance and lesser
>> memory footprint.
>>
>> The improvement is ~11x for a benchmark updating files in a loop
>> (1040K -> 11468K updates / sec).
> 
> Nice. That's a really impressive improvement.
> 
> I've been adding io_uring test cases for automated performance
> regression testing with mmtests (open source).  I'd love to take a look
> at this test case and adapt it to mmtests, so we can pick it up and run
> it frequently.
> 
> is it something you can share?

I'll post it later.

The test is quite stupid and with the patches less than 10% of CPU
cycles go to the update machinery (against 90+ w/o), the rest is spend
for syscalling, submitting update requests, etc., so it almost hits the
limit.

Another test we can do is to measure latency b/w the point we asked a
rsrc to be removed and when it actually got destroyed/freed, e.g. tags
will help with that. It should've been improved nicely as well as it
removes the RCU grace period and other bouncing.

-- 
Pavel Begunkov