linux-kernel - Re: [PATCH RFC 0/9] nxt propagation + locking optimisation

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Message-ID: <101bed21-670c-4ade-e513-b15848ef1361@gmail.com>
Date:   Sun, 1 Mar 2020 19:41:27 +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 RFC 0/9] nxt propagation + locking optimisation

On 01/03/2020 19:23, Pavel Begunkov wrote:
> On 01/03/2020 19:18, Pavel Begunkov wrote:
>> There are several independent parts in the patchset, but bundled
>> to make a point.
>> 1-2: random stuff, that implicitly used later.
>> 3-5: restore @nxt propagation
>> 6-8: optimise locking in io_worker_handle_work()
>> 9: optimise io_uring refcounting
>>
>> The next propagation bits are done similarly as it was before, but
>> - nxt stealing is now at top-level, but not hidden in handlers
>> - ensure there is no with REQ_F_DONT_STEAL_NEXT
>>
>> [6-8] is the reason to dismiss the previous @nxt propagation appoach,
>> I didn't found a good way to do the same. Even though it looked
>> clearer and without new flag.
>>
>> Performance tested it with link-of-nops + IOSQE_ASYNC:
>>
>> link size: 100
>> orig:  501 (ns per nop)
>> 0-8:   446
>> 0-9:   416
>>
>> link size: 10
>> orig:  826
>> 0-8:   776
>> 0-9:   756
> 
> BTW, that's basically QD1, and with contention for wqe->lock the gap should be
> even wider.

And another notice: "orig" actually includes [1-5], so @nxt propagation was
working there.

>>
>> Pavel Begunkov (9):
>>   io_uring: clean up io_close
>>   io-wq: fix IO_WQ_WORK_NO_CANCEL cancellation
>>   io_uring: make submission ref putting consistent
>>   io_uring: remove @nxt from handlers
>>   io_uring: get next req on subm ref drop
>>   io-wq: shuffle io_worker_handle_work() code
>>   io-wq: io_worker_handle_work() optimise locking
>>   io-wq: optimise double lock for io_get_next_work()
>>   io_uring: pass submission ref to async
>>
>>  fs/io-wq.c    | 162 ++++++++++++----------
>>  fs/io_uring.c | 366 ++++++++++++++++++++++----------------------------
>>  2 files changed, 258 insertions(+), 270 deletions(-)
>>
> 

-- 
Pavel Begunkov