From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754252AbcFGIdx (ORCPT ); Tue, 7 Jun 2016 04:33:53 -0400 Received: from mail-pf0-f196.google.com ([209.85.192.196]:33985 "EHLO mail-pf0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751763AbcFGIdu (ORCPT ); Tue, 7 Jun 2016 04:33:50 -0400 From: Wanpeng Li X-Google-Original-From: Wanpeng Li To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Wanpeng Li , Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= , Ingo Molnar , "Peter Zijlstra (Intel)" , Rik van Riel , Thomas Gleixner , Frederic Weisbecker Subject: [PATCH v4 1/3] KVM: fix steal clock warp during guest cpu hotplug Date: Tue, 7 Jun 2016 16:33:07 +0800 Message-Id: <1465288389-3542-1-git-send-email-wanpeng.li@hotmail.com> X-Mailer: git-send-email 1.9.1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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. 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 underflow. Rik also pointed out to me: | I have seen stuff like that with live migration too, in the past The root cause of steal clock warp during hotplug is kvm_steal_time reset to 0 after cpu hotplug comes back which should be preexiting guest value. This patch fix it by don't reset kvm_steal_time during guest cpu hotplug. Suggested-by: Paolo Bonzini Cc: Paolo Bonzini Cc: Radim Krčmář Cc: Ingo Molnar Cc: Peter Zijlstra (Intel) Cc: Rik van Riel Cc: Thomas Gleixner Cc: Frederic Weisbecker Signed-off-by: Wanpeng Li --- v2 -> v3: * fix the root cause v1 -> v2: * update patch subject, description and comments * deal with the case where steal time suddenly increases by a ludicrous amount arch/x86/kernel/kvm.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index eea2a6f..1ef5e48 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -301,8 +301,6 @@ static void kvm_register_steal_time(void) if (!has_steal_clock) return; - memset(st, 0, sizeof(*st)); - wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | KVM_MSR_ENABLED)); pr_info("kvm-stealtime: cpu %d, msr %llx\n", cpu, (unsigned long long) slow_virt_to_phys(st)); -- 1.9.1