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Date:   Sun, 6 Sep 2020 20:38:20 +0200
From:   Pavel Machek <pavel@denx.de>
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     Pavel Machek <pavel@denx.de>,
        David Laight <David.Laight@ACULAB.COM>,
        Christoph Hellwig <hch@lst.de>,
        "arnd@arndb.de" <arnd@arndb.de>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] /dev/zero: also implement ->read
Message-ID: <20200906183820.GA13290@amd>
References: <20200903155922.1111551-1-hch@lst.de>
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On Sun 2020-09-06 20:35:38, Christophe Leroy wrote:
> Hi,
>=20
> Le 06/09/2020 =E0 20:21, Pavel Machek a =E9crit=A0:
> >Hi!
> >
> >>>>Christophe reported a major speedup due to avoiding the iov_iter
> >>>>overhead, so just add this trivial function.  Note that /dev/zero
> >>>>already implements both an iter and non-iter writes so this just
> >>>>makes it more symmetric.
> >>>>
> >>>>Christophe Leroy <christophe.leroy@csgroup.eu>
> >>>>Signed-off-by: Christoph Hellwig <hch@lst.de>
> >>>
> >>>Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> >>
> >>Any idea what has happened to make the 'iter' version so bad?
> >
> >Exactly. Also it would be nice to note how the speedup was measured
> >and what the speedup is.
> >
>=20
> Was measured on an 8xx powerpc running at 132MHz with:
>=20
> 	dd if=3D/dev/zero of=3D/dev/null count=3D1M
>=20
> With the patch, dd displays a throughput of 113.5MB/s
> Without the patch it is 99.9MB/s

Actually... that does not seem like a huge deal. read(/dev/zero) is
not that common operation.

Are you getting similar speedups on normal hardware?

								Pavel
--=20
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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