Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761198Ab3D3S13 (ORCPT ); Tue, 30 Apr 2013 14:27:29 -0400 Received: from a9-62.smtp-out.amazonses.com ([54.240.9.62]:41007 "EHLO a9-62.smtp-out.amazonses.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760835Ab3D3S11 (ORCPT ); Tue, 30 Apr 2013 14:27:27 -0400 Date: Tue, 30 Apr 2013 18:27:25 +0000 From: Christoph Lameter X-X-Sender: cl@gentwo.org To: Tim Chen cc: Andrew Morton , Tejun Heo , Al Viro , Dave Hansen , Andi Kleen , linux-kernel , linux-mm Subject: Re: [PATCH 1/2] Make the batch size of the percpu_counter configurable In-Reply-To: <1367344522.27102.184.camel@schen9-DESK> Message-ID: <0000013e5c32f7fd-b4bf1b22-7924-42b5-b835-eb2b5926bbf6-000000@email.amazonses.com> References: <0000013e5b24d2c5-9b899862-e2fd-4413-8094-4f1e5a0c0f62-000000@email.amazonses.com> <1367339009.27102.174.camel@schen9-DESK> <0000013e5bfd1548-a6ef7962-7b00-495b-8e83-d7a08413e165-000000@email.amazonses.com> <1367344094.27102.182.camel@schen9-DESK> <0000013e5c1377c5-49a8fca5-eb04-4e3a-a507-ce3a47fea685-000000@email.amazonses.com> <1367344522.27102.184.camel@schen9-DESK> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-SES-Outgoing: 2013.04.30-54.240.9.62 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 873 Lines: 20 On Tue, 30 Apr 2013, Tim Chen wrote: > > But you will have to dereference the pointer whenever you want the batch > > size from the hot path. Looks like it would be better to put the value > > there directly. You have a list of percpu counters that can be traversed > > to change the batch size. > > > > I have considered that. But the list is not available unless we have > CONFIG_HOTPLUG_CPU compiled in. percpu counters are performance sensitive and with the pointer you will need to reference another one increasing the cache footprint. You are touching an additional cacheline somewhere in memory frequently. Not good. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/