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From: Rik van Riel <riel@redhat.com>
To: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
Cc: 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: Wed, 2 Feb 2005 22:06:20 -0500 (EST)	[thread overview]
Message-ID: <Pine.LNX.4.61.0502022204140.2678@chimarrao.boston.redhat.com> (raw)
In-Reply-To: <20050202163110.GB23132@logos.cnet>

On Wed, 2 Feb 2005, Marcelo Tosatti wrote:

> Someone should try implementing the zeroing driver for a fast x86 PCI 
> device. :)

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.

If the page is being used immediately after it is
allocated, it may be faster to prezero the page on
the fly.  On some CPUs these writes bypass the "read
from RAM" stage and allow things to just live in cache
completely.

-- 
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it." - Brian W. Kernighan

  parent reply	other threads:[~2005-02-03  3:07 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-01-21 20:29 A scrub daemon (prezeroing) 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 [this message]
2005-02-03 23:39           ` Paul Mackerras
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
2005-02-07 19:30     ` prezeroing V6 [0/3]: Changes and overview Christoph Lameter
2005-02-07 19:31       ` prezeroing V6 [1/3]: clear_pages Christoph Lameter
2005-02-07 19:31       ` prezeroing V6 [2/3]: ScrubD Christoph Lameter
2005-02-08  0:30         ` Andrew Morton
2005-02-08  0:49           ` Christoph Lameter
2005-02-08  1:09             ` Andrew Morton
2005-02-08  1:15               ` Christoph Lameter
2005-02-08  1:35                 ` Andrew Morton
2005-02-08 16:11                   ` Christoph Lameter
2005-02-08 20:27                     ` Andrew Morton
2005-02-08 20:51                       ` Christoph Lameter
2005-02-08 23:32                         ` cliff white
2005-02-07 19:32       ` prezeroing V6 [3/3]: Altix SN2 Block Transfer Engine Zeroing Driver Christoph Lameter
  -- strict thread matches above, loose matches on Subject: below --
2005-01-22 22:30 A scrub daemon (prezeroing) Joel Soete
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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