From patchwork Wed Jun 8 03:05:08 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Wanpeng Li X-Patchwork-Id: 9163261 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id B8A1E60467 for ; Wed, 8 Jun 2016 03:06:44 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id AF3872830C for ; Wed, 8 Jun 2016 03:06:44 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id A3FE72836E; Wed, 8 Jun 2016 03:06:44 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=2.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED, DKIM_SIGNED,FREEMAIL_FROM,RCVD_IN_DNSWL_HI,T_DKIM_INVALID autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 31F7F2830C for ; Wed, 8 Jun 2016 03:06:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754530AbcFHDFx (ORCPT ); Tue, 7 Jun 2016 23:05:53 -0400 Received: from mail-pa0-f68.google.com ([209.85.220.68]:35874 "EHLO mail-pa0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753516AbcFHDFw (ORCPT ); Tue, 7 Jun 2016 23:05:52 -0400 Received: by mail-pa0-f68.google.com with SMTP id fg1so15415847pad.3; Tue, 07 Jun 2016 20:05:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=JHb4ud9giUHme1Z+UlVZjqgntq3bUSVO8J0dkjfXnPY=; b=EViMkTzNGz3ENBPOxWAF3Ks84tKURBsE6NaLDsJVs1U8J66ShLgOb8FC5cCvJsqeT+ Xq1Ob7Vc24aYRdB59Wp4K0xRXmexeVjjcZ96FwHl2m9ngY9iBRJVrTBDmAUvN4xPbrwT zfDMBOUD7gNTQt/saZ3zFBqtkAzMlQOyRc0C+OCU7hk8zLEB1ENFobW0b6z0SXN/vy5A ier4gbb7EFjLZUTOw8C+BvyGw3J1VNwlcO5D751uhbHuGKHae2B2smy/pXYUwfb3TGg6 nNhmKCpO735xKU6FIULYg+ktK70/UoQD0hZ0zX0zjCqzdBGmbFgwcg83H0yatUm+eh1C Rl8g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=JHb4ud9giUHme1Z+UlVZjqgntq3bUSVO8J0dkjfXnPY=; b=AMZEG+++thXmFCLGOvqnjN8oREOa8CF3c1dq3krUAb9VueTyBmLtUDrwSFkQPlL+GB IxQP0N1IFG9FZOfFJg7lwriWxpo7HqtzywsIsYv7eMB6ti88FWtoYbnPKIfCUM296JmL A4gYPnyG5hXLo+5U9iIPn+uft1qeTiTllM0nLStvaKNssv9oRpE3NIUQXp8W00gTdVvQ P3sLJ7ESlqb9smTnvoLtbE6HX+aoft8nmkOIeeaK7bGAtvzPsY/QY8IOijN7cdxrkWrE WGI696i2+FtJMpI4do1OhFrFO1A4ZL9wuUyu+LT/20Hsk8jgZ3ytI0IUliF++RCfqMmh V53Q== X-Gm-Message-State: ALyK8tKFoDLt8/8G8HsPXM8zMWu702nTdZWoyPwgi5KPXURuXfewNXtNQWRzd0mIhEzeTQ== X-Received: by 10.67.5.134 with SMTP id cm6mr3072736pad.93.1465355151491; Tue, 07 Jun 2016 20:05:51 -0700 (PDT) Received: from kernel.kingsoft.cn ([219.141.176.229]) by smtp.gmail.com with ESMTPSA id y70sm2368643pff.25.2016.06.07.20.05.48 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 07 Jun 2016 20:05:51 -0700 (PDT) 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 , John Stultz Subject: [PATCH v5 1/3] KVM: fix steal clock warp during guest cpu hotplug Date: Wed, 8 Jun 2016 11:05:08 +0800 Message-Id: <1465355110-21714-1-git-send-email-wanpeng.li@hotmail.com> X-Mailer: git-send-email 1.9.1 MIME-Version: 1.0 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Wanpeng Li Sometimes, after CPU hotplug you can observe a spike in stolen time (100%) followed by the CPU being marked as 100% idle when it's actually busy with a CPU hog task. The trace looks like the following: 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 sudden decrease of "steal" causes steal_jiffies to underflow. The root cause is kvm_steal_time being reset to 0 after hot-plugging back in a CPU. Instead, the preexisting value can be used, which is what the core scheduler code expects. John Stultz also reported a similar issue after guest S3. 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 Cc: John Stultz Signed-off-by: Wanpeng Li --- v4 -> v5: * improve commit message 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));