From: Peter Zijlstra Subject: Re: [PATCH] percpu_counter: Fix __percpu_counter_sum() Date: Tue, 09 Dec 2008 00:05:00 +0100 Message-ID: <1228777500.12729.4.camel@twins> References: <4936D287.6090206@cosmosbay.com> <4936EB04.8000609@cosmosbay.com> <20081206202233.3b74febc.akpm@linux-foundation.org> <493BCF60.1080409@cosmosbay.com> <20081207092854.f6bcbfae.akpm@linux-foundation.org> <493C0F40.7040304@cosmosbay.com> <20081207205250.dbb7fe4b.akpm@linux-foundation.org> <20081208221241.GA2501@mit.edu> <1228774836.16244.22.camel@lappy.programming.kicks-ass.net> <20081208230047.GC2501@mit.edu> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Andrew Morton , Eric Dumazet , linux kernel , "David S. Miller" , Mingming Cao , linux-ext4@vger.kernel.org To: Theodore Tso Return-path: Received: from viefep18-int.chello.at ([213.46.255.22]:25445 "EHLO viefep18-int.chello.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752565AbYLHXFF (ORCPT ); Mon, 8 Dec 2008 18:05:05 -0500 In-Reply-To: <20081208230047.GC2501@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, 2008-12-08 at 18:00 -0500, Theodore Tso wrote: > On Mon, Dec 08, 2008 at 11:20:35PM +0100, Peter Zijlstra wrote: > > > > atomic_t is pretty good on all archs, but you get to keep the cacheline > > ping-pong. > > > > Stupid question --- if you're worried about cacheline ping-pongs, why > aren't each cpu's delta counter cacheline aligned? With a 64-byte > cache-line, and a 32-bit counters entry, with less than 16 CPU's we're > going to be getting cache ping-pong effects with percpu_counter's, > right? Or am I missing something? sorta - a new per-cpu allocator is in the works, but we do cacheline align the per-cpu allocations (or used to), also, the allocations are node affine.