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SubjectRe: [PATCH] /dev/zero: also implement ->read

Le 06/09/2020 à 20:21, Pavel Machek a écrit :
> 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 <>
>>>> Signed-off-by: Christoph Hellwig <>
>>> Tested-by: Christophe Leroy <>
>> 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.

Was measured on an 8xx powerpc running at 132MHz with:

dd if=/dev/zero of=/dev/null count=1M

With the patch, dd displays a throughput of 113.5MB/s
Without the patch it is 99.9MB/s


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