From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753673Ab0IHTmi (ORCPT ); Wed, 8 Sep 2010 15:42:38 -0400 Received: from plane.gmane.org ([80.91.229.3]:42250 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753161Ab0IHTme (ORCPT ); Wed, 8 Sep 2010 15:42:34 -0400 From: Andi Kleen To: Cliff Wickman Cc: public-kexec-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@plane.gmane.org, public-mingo-X9Un+BFzKDI@plane.gmane.org, public-linux-kernel-u79uwXL29TY76Z2rM5mHXA@plane.gmane.org Subject: Re: [PATCH] x86: copy_oldmem_page using cached addressing References: Date: Wed, 08 Sep 2010 21:42:18 +0200 In-Reply-To: (Cliff Wickman's message of "Wed, 08 Sep 2010 10:14:27 -0500") Message-ID: <87eid4vx7p.fsf@basil.nowhere.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Cliff Wickman writes: > From: Cliff Wickman > > The copy of /proc/vmcore to a user buffer proceeds much faster > if the kernel addresses memory as cached. > > With this patch we have seen an increase in transfer rate from less than > 15MB/s to 80-460MB/s, depending on size of the transfer. This makes > a big difference in time needed to save a system dump. > > (Does anyone know of a reason why copy_oldmem_page() would need > to use uncached addresses?) > > Diffed against 2.6.36-rc3 I had a similar patch somewhere in my private kernels, yes it's a big win. I think it was simply a bug that was added when ioremap was changed to default to uncached. -Andi -- ak@linux.intel.com -- Speaking for myself only.