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Message-ID: <20090206233747.GA8747@google.com>
Date: Fri, 6 Feb 2009 15:37:47 -0800
From: Mandeep Singh Baines <msb@...gle.com>
To: mingo@...e.hu, fweisbec@...il.com
Cc: linux-kernel@...r.kernel.org, rientjes@...gle.com,
mbligh@...gle.com, thockin@...gle.com, akpm@...ux-foundation.org
Subject: [PATCH] softlockup: remove timestamp checking from hung_task
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 <msb@...gle.com>
---
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
--
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