From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH v2] sched/cputime: add steal clock warp handling Date: Mon, 6 Jun 2016 15:44:34 +0200 Message-ID: References: <1464931288-5886-1-git-send-email-wanpeng.li@hotmail.com> <1464959407.16365.120.camel@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: Wanpeng Li , Ingo Molnar , "Peter Zijlstra (Intel)" , Thomas Gleixner , Frederic Weisbecker , Radim To: Rik van Riel , Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Return-path: In-Reply-To: <1464959407.16365.120.camel@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 03/06/2016 15:10, Rik van Riel wrote: > On Fri, 2016-06-03 at 13:21 +0800, Wanpeng Li wrote: >> From: Wanpeng Li >> >> I observed that sometimes st is 100% instantaneous, then idle is >> 100% >> even if there is a cpu hog on the guest cpu after the cpu hotplug >> comes >> back(N.B. this can not always be readily reproduced). I add trace to >> capture it as below: >> >> cpuhp/1-12 [001] d.h1 167.461657: account_process_tick: steal = >> 1291385514, prev_steal_time = 0 >> cpuhp/1-12 [001] d.h1 167.461659: account_process_tick: >> steal_jiffies = 1291 >> -0 [001] d.h1 167.462663: account_process_tick: steal = >> 18732255, prev_steal_time = 1291000000 >> -0 [001] d.h1 167.462664: account_process_tick: >> steal_jiffies = 18446744072437 >> >> The steal clock warp and then steal_jiffies overflow. >> >> Rik also pointed out to me: >> >>> >>> I have seen stuff like that with live migration too, in the past >> This patch adds steal clock warp handling by a safe threshold to >> only >> apply steal times that are positive and smaller than one second (as >> long as nohz_full has the one second timer tick left), ignoring >> intervals >> that are negative or longer than a second, and using those to sync >> up >> the guest with the host. >> >> Cc: Ingo Molnar >> Cc: Peter Zijlstra (Intel) >> Cc: Rik van Riel >> Cc: Thomas Gleixner >> Cc: Frederic Weisbecker >> Cc: Paolo Bonzini >> Cc: Radim >> Signed-off-by: Wanpeng Li > > Reviewed-by: Rik van Riel Sorry for being late---again, I'd like to give a shot to a fix in KVM guest code. Paolo