From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752058AbdB0Pfa (ORCPT ); Mon, 27 Feb 2017 10:35:30 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52024 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751500AbdB0Pf2 (ORCPT ); Mon, 27 Feb 2017 10:35:28 -0500 Subject: Re: tip.today - scheduler bam boom crash (cpu hotplug) To: Peter Zijlstra References: <1484811069.17751.14.camel@gmx.de> <20170119101924.GJ6485@twins.programming.kicks-ass.net> <20170119133633.GB6536@twins.programming.kicks-ass.net> <20170227124349.GU6515@twins.programming.kicks-ass.net> <3e7c34e2-757b-19e9-f7e5-9bfaadd79e5d@redhat.com> <20170227130440.GW6500@twins.programming.kicks-ass.net> Cc: Wanpeng Li , Mike Galbraith , LKML , Ingo Molnar , Thomas Gleixner , Borislav Petkov From: Paolo Bonzini Message-ID: <15367170-e1c0-8901-7e15-940d8d699c21@redhat.com> Date: Mon, 27 Feb 2017 16:27:32 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <20170227130440.GW6500@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Mon, 27 Feb 2017 15:27:35 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 27/02/2017 14:04, Peter Zijlstra wrote: >>>> This results in sched clock always unstable for kvm guest since there >>>> is no invariant tsc cpuid bit exposed for kvm guest currently. >>> What the heck is KVM_FEATURE_CLOCKSOURCE_STABLE_BIT / >>> PVCLOCK_TSC_STABLE_BIT about then? >> It checks that all the bugs in the host have been ironed out, and that >> the host itself supports invtsc. > But what does it mean if that is not so? That is, will kvm_clock_read() > still be stable even if !stable? If kvmclock is !stable, nobody should have set that the sched clock to stable, to begin with. However, if kvmclock is stable, we know that the sched clock is stable. Paolo