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From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>, Matthew Wilcox <willy@infradead.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fs: optimise kiocb_set_rw_flags()
Date: Sun, 2 Aug 2020 11:33:37 +0300
Message-ID: <48d1c305-6302-daaf-9153-8cdc85911a88@gmail.com> (raw)
In-Reply-To: <debd12e1-8ba5-723d-75ad-47af99db05a0@kernel.dk>

On 01/08/2020 20:01, Jens Axboe wrote:
> On 8/1/20 9:37 AM, Matthew Wilcox wrote:
>> On Sat, Aug 01, 2020 at 01:36:33PM +0300, Pavel Begunkov wrote:
>>> Use a local var to collect flags in kiocb_set_rw_flags(). That spares
>>> some memory writes and allows to replace most of the jumps with MOVEcc.
>>>
>>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>>
>> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
>>
>> If you want to improve the codegen here further, I would suggest that
>> renumbering the IOCB flags to match the RWF flags would lead to better
>> codegen (can't do it the other way around; RWF flags are userspace ABI,
>> IOCB flags are not).  iocb_flags() probably doesn't get any worse because
>> the IOCB_ flags don't have the same numbers as the O_ bits (which differ
>> by arch anyway).
> 
> Yeah that's not a bad idea, would kill a lot of branches.

Is that common here to do so? I've done this for io_uring flags a while
ago, but left RWF alone at the time, reluctant to check for possible
complications (e.g. bit magic).

-- 
Pavel Begunkov

  reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-01 10:36 Pavel Begunkov
2020-08-01 10:42 ` Pavel Begunkov
2020-08-01 15:37 ` Matthew Wilcox
2020-08-01 17:01   ` Jens Axboe
2020-08-02  8:33     ` Pavel Begunkov [this message]
2020-08-02  8:41   ` Pavel Begunkov
2020-08-01 17:02 ` Jens Axboe
2020-08-02  8:21   ` Pavel Begunkov
  -- strict thread matches above, loose matches on Subject: below --
2020-01-17  1:16 Pavel Begunkov
2020-01-17  1:21 ` Matthew Wilcox
2020-01-17  1:23   ` Pavel Begunkov

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