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From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
To: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Alexander Kuleshov <kuleshovmail@gmail.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fs/fat: calculate checksum in a loop instead of directly calculating
Date: Tue, 24 Feb 2015 11:42:39 +0900	[thread overview]
Message-ID: <8761asni74.fsf@mail.parknet.co.jp> (raw)
In-Reply-To: <54EB905B.8010704@gmx.de> (Heinrich Schuchardt's message of "Mon, 23 Feb 2015 21:40:59 +0100")

Heinrich Schuchardt <xypron.glpk@gmx.de> writes:

> You have to put
> __attribute__((optimize("unroll-loops")))
> here to unroll the loop inside the function:
>
>
> static __attribute__ ((noinline))
> __attribute__((optimize("unroll-loops")))
> int test(unsigned char *name)
>
> $ time ./c.inline aaaaaaaaaaa
> 14
>
> real    0m0.743s
> user    0m0.740s
> sys     0m0.000s
>
> Without __attribute__((optimize("unroll-loops"))) :
> $ time ./c.loop aaaaaaaaaaa
> 14
>
> real    0m1.482s
> user    0m1.472s
> sys     0m0.004s
>
> With __attribute__((optimize("unroll-loops"))) :
>
> $ time ./c.loop aaaaaaaaaaa
> 14
>
> real    0m0.742s
> user    0m0.740s
> sys     0m0.000s

This attribute has to be added to the caller, not fat_checksum()?  I.e.,
we has to add it to all callers of fat_checksum()?

Well, this is interesting gcc optimize option though, maybe not worth to
introduce this to kernel only for fatfs.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

  reply	other threads:[~2015-02-24  2:42 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-18 18:48 [PATCH] fs/fat: calculate checksum in a loop instead of directly calculating Alexander Kuleshov
2015-02-18 19:25 ` OGAWA Hirofumi
2015-02-18 19:46   ` Alexander Kuleshov
2015-02-18 20:32     ` OGAWA Hirofumi
2015-02-23 20:40       ` Heinrich Schuchardt
2015-02-24  2:42         ` OGAWA Hirofumi [this message]
2015-02-24 19:22           ` Heinrich Schuchardt

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