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Subject: Re: [PATCH] fs: optimise kiocb_set_rw_flags()
To:     Matthew Wilcox <willy@infradead.org>,
        Pavel Begunkov <asml.silence@gmail.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
References: <e523f51f59ad6ecdad4ad22c560cb9c913e96e1a.1596277420.git.asml.silence@gmail.com>
 <20200801153711.GV23808@casper.infradead.org>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <debd12e1-8ba5-723d-75ad-47af99db05a0@kernel.dk>
Date:   Sat, 1 Aug 2020 11:01:38 -0600
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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.

-- 
Jens Axboe