linux-kernel - Re: [PATCH] /dev/zero: also implement ->read

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Message-ID: <20200906182122.GA12295@amd>
Date:   Sun, 6 Sep 2020 20:21:22 +0200
From:   Pavel Machek <pavel@...x.de>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Christophe Leroy' <christophe.leroy@...roup.eu>,
        Christoph Hellwig <hch@....de>,
        "arnd@...db.de" <arnd@...db.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] /dev/zero: also implement ->read

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@...roup.eu>
> > > Signed-off-by: Christoph Hellwig <hch@....de>
> > 
> > Tested-by: Christophe Leroy <christophe.leroy@...roup.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.

Best regads,
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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