From: Paul Mackerras <paulus@samba.org>
To: Rik van Riel <riel@redhat.com>
Cc: Marcelo Tosatti <marcelo.tosatti@cyclades.com>,
Christoph Lameter <clameter@sgi.com>,
David Woodhouse <dwmw2@infradead.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@osdl.org
Subject: Re: A scrub daemon (prezeroing)
Date: Fri, 4 Feb 2005 10:39:10 +1100 [thread overview]
Message-ID: <16898.46622.108835.631425@cargo.ozlabs.ibm.com> (raw)
In-Reply-To: <Pine.LNX.4.61.0502022204140.2678@chimarrao.boston.redhat.com>
Rik van Riel writes:
> I'm not convinced. Zeroing a page takes 2000-4000 CPU
> cycles, while faulting the page from RAM into cache takes
> 200-400 CPU cycles per cache line, or 6000-12000 CPU
> cycles.
On my G5 it takes ~200 cycles to zero a whole page. In other words it
takes about the same time to zero a page as to bring in a single cache
line from memory. (PPC has an instruction to establish a whole cache
line of zeroes in modified state without reading anything from
memory.)
Thus I can't see how prezeroing can ever be a win on ppc64.
Regards,
Paul.
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next prev parent reply other threads:[~2005-02-03 23:39 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-01-21 20:29 Christoph Lameter
2005-01-27 12:15 ` David Woodhouse
2005-01-27 13:12 ` Robin Holt
2005-01-27 13:14 ` David Woodhouse
2005-01-27 17:02 ` Christoph Lameter
2005-02-08 11:31 ` Ralf Baechle
2005-02-02 15:32 ` Marcelo Tosatti
2005-02-02 19:05 ` Christoph Lameter
2005-02-02 16:31 ` Marcelo Tosatti
2005-02-02 21:31 ` Christoph Lameter
2005-02-02 21:39 ` David Woodhouse
2005-02-03 3:06 ` Rik van Riel
2005-02-03 23:39 ` Paul Mackerras [this message]
2005-02-04 0:59 ` Christoph Lameter
2005-02-04 5:30 ` Paul Mackerras
2005-02-04 6:26 ` Christoph Lameter
2005-02-04 6:43 ` Nick Piggin
2005-02-04 6:50 ` Christoph Lameter
2005-02-04 9:20 ` Paul Mackerras
2005-02-04 9:28 ` Andi Kleen
2005-02-04 17:02 ` Christoph Lameter
2005-02-04 22:25 ` Paul Mackerras
2005-02-02 21:00 ` Maciej W. Rozycki
2005-02-02 21:33 ` David Woodhouse
-- strict thread matches above, loose matches on Subject: below --
2005-01-04 23:13 Prezeroing V3 [1/4]: Allow request for zeroed memory Christoph Lameter
2005-01-08 21:12 ` Hugh Dickins
2005-01-08 21:56 ` David S. Miller
2005-01-21 20:15 ` A scrub daemon (prezeroing) Christoph Lameter
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