From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754412AbcESPGm (ORCPT ); Thu, 19 May 2016 11:06:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60464 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753782AbcESPGl (ORCPT ); Thu, 19 May 2016 11:06:41 -0400 Subject: Re: [PATCH v2] KVM: halt-polling: poll if emulated lapic timer will fire soon To: Christian Borntraeger , Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <1463664426-2991-1-git-send-email-wanpeng.li@hotmail.com> <19abf5c8-7016-45af-f0e6-3bdd161ffb38@redhat.com> <573DD312.4060001@de.ibm.com> <573DD5C9.2000108@de.ibm.com> Cc: Wanpeng Li , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , David Matlack From: Paolo Bonzini Message-ID: <83e82f6b-bc6b-a85b-e2c7-9a1b4d4997d1@redhat.com> Date: Thu, 19 May 2016 17:06:33 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.0 MIME-Version: 1.0 In-Reply-To: <573DD5C9.2000108@de.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Thu, 19 May 2016 15:06:40 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/05/2016 17:03, Christian Borntraeger wrote: > > > Would this work too and be simpler? > > > Hmm, your patch does only fiddle with the grow/shrink logic (which might > > > be a good idea independently of this change), but the original patch > > > actually takes into account that we have a guaranteed maximum time by a > > > wakeup timer - IOW we know exactly what the maximum poll time is. > > > > Yes, it's different. The question is whether a 10us poll (40,000 clock > > cycles) has an impact even if it's sometimes wrong. > > Valid question. As I said, this change might be something good independent from > the original patch. (it might make it unnecessary, though) On the other hand > I can handle ~30 guest entry/exit cycles of a simple exit like diag9c. > Needs measurement. Actually I'm okay with the original patch, and especially on s390 where the maximum poll time is small it may make a bigger difference. Though I suppose the timer interrupt is not floating? Since it's not 4.7 material, I'll wait for your experiments and David's remarks. Paolo