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Subject: Re: [PATCH v3 0/6] add persistent submission state
To:     Pavel Begunkov <asml.silence@gmail.com>, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org
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From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <1124e9e0-cf3b-767e-40a5-57297e5ec17b@kernel.dk>
Date:   Fri, 31 Jan 2020 19:10:41 -0700
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On 1/31/20 5:31 PM, Pavel Begunkov wrote:
> On 01/02/2020 01:32, Pavel Begunkov wrote:
>> On 01/02/2020 01:22, Jens Axboe wrote:
>>> On 1/31/20 3:15 PM, Pavel Begunkov wrote:
>>>> Apart from unrelated first patch, this persues two goals:
>>>>
>>>> 1. start preparing io_uring to move resources handling into
>>>> opcode specific functions
>>>>
>>>> 2. make the first step towards long-standing optimisation ideas
>>>>
>>>> Basically, it makes struct io_submit_state embedded into ctx, so
>>>> easily accessible and persistent, and then plays a bit around that.
>>>
>>> Do you have any perf/latency numbers for this? Just curious if we
>>> see any improvements on that front, cross submit persistence of
>>> alloc caches should be a nice sync win, for example, or even
>>> for peak iops by not having to replenish the pool for each batch.
>>>
>>> I can try and run some here too.
>>>
>>
>> I tested the first version, but my drive is too slow, so it was only nops and
>> hence no offloading. Honestly, there waren't statistically significant results.
>> I'll rerun anyway.
>>
>> I have a plan to reuse it for a tricky optimisation, but thinking twice, I can
>> just stash it until everything is done. That's not the first thing in TODO and
>> will take a while.
>>
> 
> I've got numbers, but there is nothing really interesting. Throughput is
> insignificantly better with the patches, but I'd need much more experiments
> across reboots to confirm that.
> 
> Let's postpone the patchset for later

Sounds fine to me, no need to do it unless it's a nice cleanup, and/or
provides some nice improvements.

It would be great to see the splice stuff revamped, though :-)

-- 
Jens Axboe