From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anna Schumaker <Anna.Schumaker-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH v1 0/8] VFS: In-kernel copy system call
Date: Tue, 8 Sep 2015 11:08:03 -0400
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To: Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>,
	Andreas Dilger <adilger-m1MBpc4rdrD3fQ9qLvQP4Q@public.gmane.org>
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On 09/05/2015 04:33 AM, Al Viro wrote:
> On Fri, Sep 04, 2015 at 04:25:27PM -0600, Andreas Dilger wrote:
> 
>> This is a bit of a surprising result, since in my testing in the
>> past, copy_{to/from}_user() is a major consumer of CPU time (50%
>> of a CPU core at 1GB/s).  What backing filesystem did you test on?
> 
> While we are at it, was cp(1) using read(2)/write(2) loop or was it using
> something else (sendfile(2), for example)?

cp uses a read / write loop, and has some heuristics for guessing an optimum buffer size.

Anna

>