From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: Software prefetching considered harmful Date: Fri, 20 May 2011 11:42:49 +1000 Message-ID: <1305855769.7481.114.camel@pasglop> References: Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from gate.crashing.org ([63.228.1.57]:47634 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934716Ab1ETBnV (ORCPT ); Thu, 19 May 2011 21:43:21 -0400 In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Linus Torvalds Cc: linux-arch@vger.kernel.org, Ingo Molnar , David Miller , Russell King On Thu, 2011-05-19 at 12:05 -0700, Linus Torvalds wrote: > On Thu, May 19, 2011 at 10:12 AM, Linus Torvalds > 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.