From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932592AbcFBL5e (ORCPT ); Thu, 2 Jun 2016 07:57:34 -0400 Received: from mail-pf0-f195.google.com ([209.85.192.195]:33588 "EHLO mail-pf0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751709AbcFBL5b (ORCPT ); Thu, 2 Jun 2016 07:57:31 -0400 From: Wanpeng Li X-Google-Original-From: Wanpeng Li To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Wanpeng Li , Ingo Molnar , "Peter Zijlstra (Intel)" , Rik van Riel , Thomas Gleixner , Frederic Weisbecker , Paolo Bonzini , Radim Subject: [PATCH] sched/cputime: add steal clock warps handling during cpu hotplug Date: Thu, 2 Jun 2016 19:57:19 +0800 Message-Id: <1464868639-8924-1-git-send-email-wanpeng.li@hotmail.com> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. both guest and host are latest 4.7-rc1, 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 warps and then steal_jiffies overflow, this patch align prev_steal_time to the new steal clock timestamp, in order to avoid overflow and st stuff can continue to work. 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 --- kernel/sched/cputime.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 75f98c5..d0eebc3 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -265,7 +265,13 @@ static __always_inline bool steal_account_process_tick(void) unsigned long steal_jiffies; steal = paravirt_steal_clock(smp_processor_id()); - steal -= this_rq()->prev_steal_time; + if (likely(steal > this_rq()->prev_steal_time)) + steal -= this_rq()->prev_steal_time; + else { + /* steal clock warp */ + this_rq()->prev_steal_time = steal; + return false; + } /* * steal is in nsecs but our caller is expecting steal -- 1.9.1