From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756838AbZBGBWW (ORCPT ); Fri, 6 Feb 2009 20:22:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752619AbZBGBWL (ORCPT ); Fri, 6 Feb 2009 20:22:11 -0500 Received: from smtp-out.google.com ([216.239.45.13]:51010 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752440AbZBGBWJ (ORCPT ); Fri, 6 Feb 2009 20:22:09 -0500 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=date:from:to:cc:subject:message-id:mime-version: content-type:content-disposition:x-operating-system:user-agent: x-gmailtapped-by:x-gmailtapped; b=xWDaEQoHRtR2NEHVciILFm1DcQafI3Nxvs4UfhC+M6Zci8i6edJCJdFSLuspnX0s2 njGLrJHjQt13Ihu07ZyFA== Date: Fri, 6 Feb 2009 15:37:47 -0800 From: Mandeep Singh Baines To: mingo@elte.hu, fweisbec@gmail.com Cc: linux-kernel@vger.kernel.org, rientjes@google.com, mbligh@google.com, thockin@google.com, akpm@linux-foundation.org Subject: [PATCH] softlockup: remove timestamp checking from hung_task Message-ID: <20090206233747.GA8747@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Operating-System: Linux/2.6.18.5-gg42workstation-mixed64-32 (x86_64) User-Agent: Mutt/1.5.11 X-GMailtapped-By: 172.28.16.76 X-GMailtapped: msb Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Patch against tip/core/softlockup --- Impact: saves sizeof(long) bytes per task_struct By guaranteeing that sysctl_hung_task_timeout_secs have elapsed between tasklist scans we can avoid using timestamps. Signed-off-by: Mandeep Singh Baines --- include/linux/sched.h | 1 - kernel/fork.c | 8 +++----- kernel/hung_task.c | 48 +++++++++--------------------------------------- 3 files changed, 12 insertions(+), 45 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 2a2811c..e0d723f 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1241,7 +1241,6 @@ struct task_struct { #endif #ifdef CONFIG_DETECT_HUNG_TASK /* hung task detection */ - unsigned long last_switch_timestamp; unsigned long last_switch_count; #endif /* CPU-specific state of this task */ diff --git a/kernel/fork.c b/kernel/fork.c index fb94442..bf582f7 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -639,6 +639,9 @@ static int copy_mm(unsigned long clone_flags, struct task_struct * tsk) tsk->min_flt = tsk->maj_flt = 0; tsk->nvcsw = tsk->nivcsw = 0; +#ifdef CONFIG_DETECT_HUNG_TASK + tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw; +#endif tsk->mm = NULL; tsk->active_mm = NULL; @@ -1041,11 +1044,6 @@ static struct task_struct *copy_process(unsigned long clone_flags, p->default_timer_slack_ns = current->timer_slack_ns; -#ifdef CONFIG_DETECT_HUNG_TASK - p->last_switch_count = 0; - p->last_switch_timestamp = 0; -#endif - task_io_accounting_init(&p->ioac); acct_clear_integrals(p); diff --git a/kernel/hung_task.c b/kernel/hung_task.c index 3951a80..4a10756 100644 --- a/kernel/hung_task.c +++ b/kernel/hung_task.c @@ -34,7 +34,6 @@ unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT; * Zero means infinite timeout - no checking done: */ unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120; -static unsigned long __read_mostly hung_task_poll_jiffies; unsigned long __read_mostly sysctl_hung_task_warnings = 10; @@ -69,33 +68,17 @@ static struct notifier_block panic_block = { .notifier_call = hung_task_panic, }; -/* - * Returns seconds, approximately. We don't need nanosecond - * resolution, and we don't need to waste time with a big divide when - * 2^30ns == 1.074s. - */ -static unsigned long get_timestamp(void) -{ - int this_cpu = raw_smp_processor_id(); - - return cpu_clock(this_cpu) >> 30LL; /* 2^30 ~= 10^9 */ -} - -static void check_hung_task(struct task_struct *t, unsigned long now, - unsigned long timeout) +static void check_hung_task(struct task_struct *t, unsigned long timeout) { unsigned long switch_count = t->nvcsw + t->nivcsw; if (t->flags & PF_FROZEN) return; - if (switch_count != t->last_switch_count || !t->last_switch_timestamp) { + if (switch_count != t->last_switch_count) { t->last_switch_count = switch_count; - t->last_switch_timestamp = now; return; } - if ((long)(now - t->last_switch_timestamp) < timeout) - return; if (!sysctl_hung_task_warnings) return; sysctl_hung_task_warnings--; @@ -111,7 +94,6 @@ static void check_hung_task(struct task_struct *t, unsigned long now, sched_show_task(t); __debug_show_held_locks(t); - t->last_switch_timestamp = now; touch_nmi_watchdog(); if (sysctl_hung_task_panic) @@ -145,7 +127,6 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout) { int max_count = sysctl_hung_task_check_count; int batch_count = HUNG_TASK_BATCHING; - unsigned long now = get_timestamp(); struct task_struct *g, *t; /* @@ -168,19 +149,16 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout) } /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ if (t->state == TASK_UNINTERRUPTIBLE) - check_hung_task(t, now, timeout); + check_hung_task(t, timeout); } while_each_thread(g, t); unlock: rcu_read_unlock(); } -static void update_poll_jiffies(void) +static unsigned long timeout_jiffies(unsigned long timeout) { /* timeout of 0 will disable the watchdog */ - if (sysctl_hung_task_timeout_secs == 0) - hung_task_poll_jiffies = MAX_SCHEDULE_TIMEOUT; - else - hung_task_poll_jiffies = sysctl_hung_task_timeout_secs * HZ / 2; + return (timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT); } /* @@ -197,8 +175,6 @@ int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, if (ret || !write) goto out; - update_poll_jiffies(); - wake_up_process(watchdog_task); out: @@ -211,20 +187,14 @@ int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, static int watchdog(void *dummy) { set_user_nice(current, 0); - update_poll_jiffies(); for ( ; ; ) { - unsigned long timeout; + unsigned long timeout = sysctl_hung_task_timeout_secs; - while (schedule_timeout_interruptible(hung_task_poll_jiffies)); + while (schedule_timeout_interruptible(timeout_jiffies(timeout))) + timeout = sysctl_hung_task_timeout_secs; - /* - * Need to cache timeout here to avoid timeout being set - * to 0 via sysctl while inside check_hung_*_tasks(). - */ - timeout = sysctl_hung_task_timeout_secs; - if (timeout) - check_hung_uninterruptible_tasks(timeout); + check_hung_uninterruptible_tasks(timeout); } return 0; -- 1.5.4.5