From: Pavel Begunkov <asml.silence@gmail.com>
To: 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: Fri, 17 Jan 2020 04:23:55 +0300 [thread overview]
Message-ID: <8cecd243-38aa-292d-15cd-49b485f9253f@gmail.com> (raw)
In-Reply-To: <20200117012123.GA9226@bombadil.infradead.org>
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On 17/01/2020 04:21, Matthew Wilcox wrote:
> On Fri, Jan 17, 2020 at 04:16:41AM +0300, Pavel Begunkov wrote:
>> kiocb_set_rw_flags() generates a poor code with several memory writes
>> and a lot of jumps. Help compilers to optimise it.
>>
>> Tested with gcc 9.2 on x64-86, and as a result, it its output now is a
>> plain code without jumps accumulating in a register before a memory
>> write.
>
> Nice!
>
>> static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
>> {
>> + int kiocb_flags = 0;
>> +
>> if (unlikely(flags & ~RWF_SUPPORTED))
>> return -EOPNOTSUPP;
>>
>> if (flags & RWF_NOWAIT) {
>> if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
>> return -EOPNOTSUPP;
>> - ki->ki_flags |= IOCB_NOWAIT;
>> + kiocb_flags |= IOCB_NOWAIT;
>> }
>> if (flags & RWF_HIPRI)
>> - ki->ki_flags |= IOCB_HIPRI;
>> + kiocb_flags |= IOCB_HIPRI;
>> if (flags & RWF_DSYNC)
>> - ki->ki_flags |= IOCB_DSYNC;
>> + kiocb_flags |= IOCB_DSYNC;
>> if (flags & RWF_SYNC)
>> - ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
>> + kiocb_flags |= (IOCB_DSYNC | IOCB_SYNC);
>> if (flags & RWF_APPEND)
>> - ki->ki_flags |= IOCB_APPEND;
>> + kiocb_flags |= IOCB_APPEND;
>> +
>> + if (kiocb_flags)
>> + ki->ki_flags |= kiocb_flags;
>> return 0;
>> }
>
> Might it generate even better code to do ...
Good idea, thanks! I'll resend
>
> int kiocb_flags = 0;
>
> + if (!flags)
> + return 0;
> if (unlikely(flags & ~RWF_SUPPORTED))
> return -EOPNOTSUPP;
>
> ...
>
> - if (kiocb_flags)
> - ki->ki_flags |= kiocb_flags;
> + ki->ki_flags |= kiocb_flags;
>
--
Pavel Begunkov
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next prev parent reply other threads:[~2020-01-17 1:24 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-17 1:16 [PATCH] fs: optimise kiocb_set_rw_flags() Pavel Begunkov
2020-01-17 1:21 ` Matthew Wilcox
2020-01-17 1:23 ` Pavel Begunkov [this message]
2020-01-17 1:32 ` [PATCH v2] " Pavel Begunkov
2020-01-31 13:01 ` Pavel Begunkov
2020-02-12 12:57 ` Pavel Begunkov
2020-08-01 10:36 [PATCH] " 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
2020-08-02 8:41 ` Pavel Begunkov
2020-08-01 17:02 ` Jens Axboe
2020-08-02 8:21 ` Pavel Begunkov
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