Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758264AbbKSKec (ORCPT ); Thu, 19 Nov 2015 05:34:32 -0500 Received: from www.linutronix.de ([62.245.132.108]:39224 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758230AbbKSKea (ORCPT ); Thu, 19 Nov 2015 05:34:30 -0500 Date: Thu, 19 Nov 2015 11:33:47 +0100 (CET) From: Thomas Gleixner To: Russell King - ARM Linux cc: Marc Gonzalez , Daniel Lezcano , LKML , Mans Rullgard , Viresh Kumar , Nicolas Pitre , Tony Lindgren , Sebastian Frias Subject: Re: [PATCH] clocksource: Store reg field within struct clocksource In-Reply-To: <20151118172114.GS8644@n2100.arm.linux.org.uk> Message-ID: References: <564C8086.80804@sigmadesigns.com> <20151118172114.GS8644@n2100.arm.linux.org.uk> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1274 Lines: 35 Russell, On Wed, 18 Nov 2015, Russell King - ARM Linux wrote: > On Wed, Nov 18, 2015 at 02:43:34PM +0100, Marc Gonzalez wrote: > > Since 'struct clocksource' is ____cacheline_aligned, gcc must insert > > a lot of padding between reg and clksrc in 'struct clocksource_mmio' > > (for example, L1_CACHE_BYTES = 64 on ARMv7). > > > > Storing reg within 'struct clocksource' removes unnecessary padding, > > and reg can then be grouped with other hot data. A nice side-effect > > of this patch is making container_of() unnecessary, which makes the > > code a bit simpler. > > > > On 32-bit platforms, reg fits in the padding between read and mask, > > meaning no downside from storing it there. > > Just swap the order of 'reg' and 'clksrc'. That might reduce the memory footprint, but it does not bring the iomem pointer closer to the other hotpath clocksource data. So we still need to touch at minimum two cache lines for reading the time. With Marcs change we have all hotpath data in a single cacheline. Thanks, tglx -- 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/