Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932714AbcDBB0A (ORCPT ); Fri, 1 Apr 2016 21:26:00 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:54174 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932537AbcDBAz4 (ORCPT ); Fri, 1 Apr 2016 20:55:56 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Chris Friesen , Peter Zijlstra , Frederic Weisbecker , Linus Torvalds , Ingo Molnar , Kamal Mostafa Subject: [PATCH 3.19.y-ckt 070/170] sched/cputime: Fix steal_account_process_tick() to always return jiffies Date: Fri, 1 Apr 2016 17:52:36 -0700 Message-Id: <1459558456-24452-71-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1459558456-24452-1-git-send-email-kamal@canonical.com> References: <1459558456-24452-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.19 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2725 Lines: 74 3.19.8-ckt18 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Chris Friesen commit f9c904b7613b8b4c85b10cd6b33ad41b2843fa9d upstream. The callers of steal_account_process_tick() expect it to return whether a jiffy should be considered stolen or not. Currently the return value of steal_account_process_tick() is in units of cputime, which vary between either jiffies or nsecs depending on CONFIG_VIRT_CPU_ACCOUNTING_GEN. If cputime has nsecs granularity and there is a tiny amount of stolen time (a few nsecs, say) then we will consider the entire tick stolen and will not account the tick on user/system/idle, causing /proc/stats to show invalid data. The fix is to change steal_account_process_tick() to accumulate the stolen time and only account it once it's worth a jiffy. (Thanks to Frederic Weisbecker for suggestions to fix a bug in my first version of the patch.) Signed-off-by: Chris Friesen Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Thomas Gleixner Cc: Frederic Weisbecker Cc: Linus Torvalds Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/56DBBDB8.40305@mail.usask.ca Signed-off-by: Ingo Molnar Signed-off-by: Kamal Mostafa --- kernel/sched/cputime.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 8394b1e..87b8576 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -259,21 +259,21 @@ static __always_inline bool steal_account_process_tick(void) #ifdef CONFIG_PARAVIRT if (static_key_false(¶virt_steal_enabled)) { u64 steal; - cputime_t steal_ct; + unsigned long steal_jiffies; steal = paravirt_steal_clock(smp_processor_id()); steal -= this_rq()->prev_steal_time; /* - * cputime_t may be less precise than nsecs (eg: if it's - * based on jiffies). Lets cast the result to cputime + * steal is in nsecs but our caller is expecting steal + * time in jiffies. Lets cast the result to jiffies * granularity and account the rest on the next rounds. */ - steal_ct = nsecs_to_cputime(steal); - this_rq()->prev_steal_time += cputime_to_nsecs(steal_ct); + steal_jiffies = nsecs_to_jiffies(steal); + this_rq()->prev_steal_time += jiffies_to_nsecs(steal_jiffies); - account_steal_time(steal_ct); - return steal_ct; + account_steal_time(jiffies_to_cputime(steal_jiffies)); + return steal_jiffies; } #endif return false; -- 2.7.4