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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-arch@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
	David Miller <davem@davemloft.net>,
	Russell King <rmk@arm.linux.org.uk>
Subject: Re: Software prefetching considered harmful
Date: Fri, 20 May 2011 11:42:49 +1000	[thread overview]
Message-ID: <1305855769.7481.114.camel@pasglop> (raw)
In-Reply-To: <BANLkTi=428+KWmDcHoFYs5gO_C9wyhxJnQ@mail.gmail.com>

On Thu, 2011-05-19 at 12:05 -0700, Linus Torvalds wrote:
> On Thu, May 19, 2011 at 10:12 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > Now, notice that right now I'm *only* talking about removing it for
> > the "hlist" cases (patch attached). I suspect we should do the same
> > thing for all the list helpers.
> 
> Actually, it's the "rcu" versions of the hlist helpers that need this
> most, since those are the performance-critical ones and the ones used
> in avc traversal. So the previous patch did nothing.
> 
> So here's the actual patch I think I should commit.
> 
> Added davem, benh and rmk explicitly - I think you're on linux-arch,
> but still..  You may have machines that like prefetch more, although I
> think the "pollute the L1 cache" issue means that even if  you don't
> have the NULL pointer microtrap issue you'll still find this actually
> performs better..

Asked our local performance god:

Anton Blanchard: yeah we found this 5 years ago, i thought intel were filtering null prefetches
Anton Blanchard: turns out they werent. funny

:-)

Cheers,
Ben.

  parent reply	other threads:[~2011-05-20  1:43 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-05-19 17:12 Software prefetching considered harmful Linus Torvalds
2011-05-19 19:05 ` Linus Torvalds
2011-05-19 19:28   ` Ingo Molnar
2011-05-21  3:37     ` Michael Cree
2011-05-21  4:18       ` Benjamin Herrenschmidt
2011-05-21 10:42         ` Ingo Molnar
2011-05-19 19:32   ` David Miller
2011-05-19 19:38     ` Linus Torvalds
2011-05-19 19:47       ` David Miller
2011-05-19 23:34         ` Ingo Molnar
2011-05-20 16:01           ` Catalin Marinas
2011-05-20  1:42   ` Benjamin Herrenschmidt [this message]
2011-05-20  8:34     ` Ingo Molnar
2011-05-20  9:13       ` Benjamin Herrenschmidt

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