From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756340Ab2FNSFh (ORCPT ); Thu, 14 Jun 2012 14:05:37 -0400 Received: from smtp.citrix.com ([66.165.176.89]:12125 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753083Ab2FNSFg (ORCPT ); Thu, 14 Jun 2012 14:05:36 -0400 X-IronPort-AV: E=Sophos;i="4.75,770,1330923600"; d="scan'208";a="28120282" Message-ID: <4FDA27ED.1080404@citrix.com> Date: Thu, 14 Jun 2012 19:05:33 +0100 From: David Vrabel User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20120428 Icedove/3.0.11 MIME-Version: 1.0 To: Konrad Rzeszutek Wilk CC: "xen-devel@lists.xensource.com" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "H. Peter Anvin" Subject: Re: [PATCH] x86/xen: avoid updating TLS descriptors if they haven't changed References: <1339088494-23528-1-git-send-email-david.vrabel@citrix.com> <4FD9FAA3.6090303@citrix.com> <20120614164926.GC333@phenom.dumpdata.com> In-Reply-To: <20120614164926.GC333@phenom.dumpdata.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 14/06/12 17:49, Konrad Rzeszutek Wilk wrote: > On Thu, Jun 14, 2012 at 03:52:19PM +0100, David Vrabel wrote: >> On 07/06/12 18:01, David Vrabel wrote: >>> From: David Vrabel >>> >>> When switching tasks in a Xen PV guest, avoid updating the TLS >>> descriptors if they haven't changed. This improves the speed of >>> context switches by almost 10% as much of the time the descriptors are >>> the same or only one is different. >>> >>> The descriptors written into the GDT by Xen are modified from the >>> values passed in the update_descriptor hypercall so we keep shadow >>> copies of the three TLS descriptors to compare against. >>> >>> lmbench3 test Before After Improvement >>> -------------------------------------------- >>> lat_ctx -s 32 24 7.19 6.52 9% >>> lat_pipe 12.56 11.66 7% >>> >>> Signed-off-by: David Vrabel >>> --- >>> I note that the comment in asm/desc_defs.h says the 'a' and 'b' fields >>> in desc_struct as deprecated but there seems to be no suitable >>> alternatives. >> >> ping? Any opinion on this patch from the x86 side? If it's okay can we >> get an ack so Konrad can take the patch via his tree. > > It breaks my all my bootup tests - so NACK until at least that is fixed. > I think I sent you the whole serial log - is there something else that would help > narrow it down? You're mixing up this patch with "xen/mm: do direct hypercall in xen_set_pte() if batching is unavailable" which is broken on 64-bit and I am looking into it. David