Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161247AbWBUBD7 (ORCPT ); Mon, 20 Feb 2006 20:03:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161248AbWBUBD7 (ORCPT ); Mon, 20 Feb 2006 20:03:59 -0500 Received: from ns1.siteground.net ([207.218.208.2]:64209 "EHLO serv01.siteground.net") by vger.kernel.org with ESMTP id S1161247AbWBUBD7 (ORCPT ); Mon, 20 Feb 2006 20:03:59 -0500 Date: Mon, 20 Feb 2006 17:04:30 -0800 From: Ravikiran G Thirumalai To: Andrew Morton Cc: linux-kernel@vger.kernel.org, shai@scalex86.org Subject: Re: [patch] Cache align futex hash buckets Message-ID: <20060221010430.GE3594@localhost.localdomain> References: <20060220233242.GC3594@localhost.localdomain> <20060220153320.793b6a7d.akpm@osdl.org> <20060220153419.5ea8dd89.akpm@osdl.org> <20060221000924.GD3594@localhost.localdomain> <20060220162317.5c7b9778.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060220162317.5c7b9778.akpm@osdl.org> User-Agent: Mutt/1.4.2.1i X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - serv01.siteground.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - scalex86.org X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1740 Lines: 42 On Mon, Feb 20, 2006 at 04:23:17PM -0800, Andrew Morton wrote: > Ravikiran G Thirumalai wrote: > > > > On Mon, Feb 20, 2006 at 03:34:19PM -0800, Andrew Morton wrote: > > > Andrew Morton wrote: > > > > > > > > > @@ -100,9 +100,10 @@ struct futex_q { > > > > > struct futex_hash_bucket { > > > > > spinlock_t lock; > > > > > struct list_head chain; > > > > > -}; > > > > > +} ____cacheline_internodealigned_in_smp; > > > > > > > > > > -static struct futex_hash_bucket futex_queues[1< > > > > +static struct futex_hash_bucket futex_queues[1< > > > > + __cacheline_aligned_in_smp; > > > > > > > > > > > > > How much memory does that thing end up consuming? > > > > > > I think a megabyte? > > > > On most machines it would be 256 * 128 = 32k. or 16k on arches with 64B > > cachelines. This looked like a simpler solution for spinlocks falling on > > the same cacheline. So is 16/32k unreasonable? > > > > CONFIG_X86_VSMP enables 4096-byte padding for > ____cacheline_internodealigned_in_smp. It's a megabyte. Yes, only on vSMPowered systems. Well, we have a large internode cacheline, but these machines have lots of memory too. I thought a simpler padding solution might be acceptable as futex_queues would be large only on our boxes. Maybe we can dynamically allocate spinlocks, but it would be difficult to say which node the spinlock should come from as yet. - 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/