Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754769AbcDNM32 (ORCPT ); Thu, 14 Apr 2016 08:29:28 -0400 Received: from www.linutronix.de ([62.245.132.108]:47949 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753781AbcDNM31 (ORCPT ); Thu, 14 Apr 2016 08:29:27 -0400 From: Sebastian Andrzej Siewior To: Ingo Molnar , Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Sebastian Andrzej Siewior , Peter Zijlstra , Frederic Weisbecker , Rik van Riel , Thomas Gleixner Subject: [RFC PATCH] sched/cputime: drop local_irq_safe() in vtime_init_idle() Date: Thu, 14 Apr 2016 14:29:14 +0200 Message-Id: <1460636954-20389-1-git-send-email-bigeasy@linutronix.de> X-Mailer: git-send-email 2.8.0.rc3 X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1893 Lines: 49 A while ago vtime_init_idle() used to invoke sched_clock_cpu() and had write_seqlock_irqsave() because sched_clock_cpu() required to be called with interrupts off. This requirement is written before the body of the function and was introduced in 2010 via c676329abb2b ("sched_clock: Add local_clock() API and improve documentation"). This requirement has been dropped in 2013 via ef08f0fff876 ("sched/clock: Remove local_irq_disable() from the clocks") but the body of the function still has the comment. Now, vtime_init_idle() was converted from seqlock to seqcount via b7ce2277f087 ("sched/cputime: Convert vtime_seqlock to seqcount") and while doing so the IRQ-off region around sched_clock_cpu() was preserved while not strictly required (given the first part of this commit). A little later, sched_clock_cpu() was replaced with jiffies via ff9a9b4c4334 ("sched, time: Switch VIRT_CPU_ACCOUNTING_GEN to jiffy granularity"). Based on this events I assume it is safe to drop the local_irq_safe() section. Cc: Peter Zijlstra Cc: Frederic Weisbecker Cc: Rik van Riel Cc: Thomas Gleixner --- kernel/sched/cputime.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 75f98c5498d5..816cd4ef5873 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -785,14 +785,10 @@ void arch_vtime_task_switch(struct task_struct *prev) void vtime_init_idle(struct task_struct *t, int cpu) { - unsigned long flags; - - local_irq_save(flags); write_seqcount_begin(&t->vtime_seqcount); t->vtime_snap_whence = VTIME_SYS; t->vtime_snap = jiffies; write_seqcount_end(&t->vtime_seqcount); - local_irq_restore(flags); } cputime_t task_gtime(struct task_struct *t) -- 2.8.0.rc3