From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx135.postini.com [74.125.245.135]) by kanga.kvack.org (Postfix) with SMTP id 8280A6B0070 for ; Wed, 4 Jul 2012 12:24:19 -0400 (EDT) Received: by ggm4 with SMTP id 4so8185884ggm.14 for ; Wed, 04 Jul 2012 09:24:18 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1341418517.2583.2252.camel@edumazet-glaptop> References: <1340389359-2407-1-git-send-email-js1304@gmail.com> <1340390729-2821-1-git-send-email-js1304@gmail.com> <1341415579.2583.2134.camel@edumazet-glaptop> <1341418517.2583.2252.camel@edumazet-glaptop> Date: Thu, 5 Jul 2012 01:24:18 +0900 Message-ID: Subject: Re: [PATCH 1/3 v2] slub: prefetch next freelist pointer in __slab_alloc() From: JoonSoo Kim Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Eric Dumazet Cc: Pekka Enberg , Christoph Lameter , linux-kernel@vger.kernel.org, linux-mm@kvack.org, David Rientjes 2012/7/5 Eric Dumazet : > On Thu, 2012-07-05 at 00:48 +0900, JoonSoo Kim wrote: >> 2012/7/5 Eric Dumazet : >> > Its the slow path. I am not convinced its useful on real workloads (not >> > a benchmark) >> > >> > I mean, if a workload hits badly slow path, some more important work >> > should be done to avoid this at a higher level. >> > >> >> In hackbench test, fast path allocation is about to 93%. >> Is it insufficient? > > 7% is insufficient I am afraid. > > One prefetch() in the fast path serves 93% of the allocations, > so added icache pressure is ok. > > One prefetch() in slow path serves 7% of the allocations, do you see the > difference ? > > Adding a prefetch() is usually a win when a benchmark uses the path one > million times per second. > > But adding prefetches also increases kernel size and it hurts globally. > (Latency of the kernel depends on its size, when cpu caches are cold) > Okay. Thanks for comments which is very helpful to me. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org