linux-kernel - Re: [PATCH 0/5] batch completion + freeing improvements

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Message-ID: <4cfeff8d-cdd2-a705-4b59-0c0e1a6c213a@gmail.com>
Date:   Tue, 14 Jul 2020 10:15:32 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] batch completion + freeing improvements

On 14/07/2020 04:08, Jens Axboe wrote:
> On 7/13/20 5:41 PM, Pavel Begunkov wrote:
>> Different batching improvements, that's it.
>>
>> Unfortunately, I don't have a decent SSD/setup at hand to
>> benchmark it properly.
> 
> I do though, but I'm not seeing any improvement with this, whereas
> some of the previous series made nice improvements... If anything
> maybe it's a bit slower.

Thanks for testing it, appreciate that. Probably, the array did
something wrong with your caches, or the 2-step approach is to blame.
I'll try to refine and/or resend parts after closer benchmarking.

> 
>> p.s. if extra 32 pointers on stack would be a problem, I wanted for
>> long to put submit_state into ctx itself.
> 
> It's getting up there... But really depends on how early in the stack,
> so 32 could _probably_ work, though usually batched on-stack counts
> are a bit lower than that.

On a fresh head 250 bytes looks too much, I agree. That considering
that io_uring is stacking on top of vfs or near that, and there are
already fast_iovec/msg.

-- 
Pavel Begunkov