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Message-ID: <20070719154254.GA24225@elte.hu>
Date: Thu, 19 Jul 2007 17:42:54 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Jeremy Fitzhardinge <jeremy@...p.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>,
stable@...nel.org, Greg KH <greg@...ah.com>,
Chris Wright <chrisw@...s-sol.org>,
Jens Axboe <jens.axboe@...cle.com>
Subject: [patch] sched: implement cpu_clock(cpu) high-speed time source
* Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> > yeah. But then it should not be using sched_clock() but CFS's new
> > rq_clock() method - which does try to construct a globally valid
> > timesource out of sched_clock(). [that fix is not backportable
> > though]
>
> Hm, that doesn't look quite right. Doesn't rq_clock measure time
> spent running? Unstolen time includes idle time too (it just excludes
> time in which a VCPU is runnable but not actually running).
generally rq_clock() also includes idle time, so it should work fine for
this purpose. So, what do you think about the patch below - does it suit
Xen's purposes?
Ingo
-------------------->
Subject: sched: implement cpu_clock(cpu) high-speed time source
From: Ingo Molnar <mingo@...e.hu>
Implement the cpu_clock(cpu) interface for kernel-internal use:
high-speed (but slightly incorrect) per-cpu clock constructed from
sched_clock().
fix up blktrace and softlockup-watchdog to use this new interface.
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
block/blktrace.c | 20 ++++++++++----------
include/linux/sched.h | 7 +++++++
kernel/sched.c | 17 +++++++++++++++++
kernel/softlockup.c | 10 ++++++----
4 files changed, 40 insertions(+), 14 deletions(-)
Index: linux/block/blktrace.c
===================================================================
--- linux.orig/block/blktrace.c
+++ linux/block/blktrace.c
@@ -41,7 +41,7 @@ static void trace_note(struct blk_trace
const int cpu = smp_processor_id();
t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
- t->time = sched_clock() - per_cpu(blk_trace_cpu_offset, cpu);
+ t->time = cpu_clock(cpu) - per_cpu(blk_trace_cpu_offset, cpu);
t->device = bt->dev;
t->action = action;
t->pid = pid;
@@ -159,7 +159,7 @@ void __blk_add_trace(struct blk_trace *b
t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
t->sequence = ++(*sequence);
- t->time = sched_clock() - per_cpu(blk_trace_cpu_offset, cpu);
+ t->time = cpu_clock(cpu) - per_cpu(blk_trace_cpu_offset, cpu);
t->sector = sector;
t->bytes = bytes;
t->action = what;
@@ -488,17 +488,17 @@ void blk_trace_shutdown(request_queue_t
}
/*
- * Average offset over two calls to sched_clock() with a gettimeofday()
+ * Average offset over two calls to cpu_clock() with a gettimeofday()
* in the middle
*/
-static void blk_check_time(unsigned long long *t)
+static void blk_check_time(unsigned long long *t, int this_cpu)
{
unsigned long long a, b;
struct timeval tv;
- a = sched_clock();
+ a = cpu_clock(this_cpu);
do_gettimeofday(&tv);
- b = sched_clock();
+ b = cpu_clock(this_cpu);
*t = tv.tv_sec * 1000000000 + tv.tv_usec * 1000;
*t -= (a + b) / 2;
@@ -510,16 +510,16 @@ static void blk_check_time(unsigned long
static void blk_trace_check_cpu_time(void *data)
{
unsigned long long *t;
- int cpu = get_cpu();
+ int this_cpu = get_cpu();
- t = &per_cpu(blk_trace_cpu_offset, cpu);
+ t = &per_cpu(blk_trace_cpu_offset, this_cpu);
/*
* Just call it twice, hopefully the second call will be cache hot
* and a little more precise
*/
- blk_check_time(t);
- blk_check_time(t);
+ blk_check_time(t, this_cpu);
+ blk_check_time(t, this_cpu);
put_cpu();
}
Index: linux/include/linux/sched.h
===================================================================
--- linux.orig/include/linux/sched.h
+++ linux/include/linux/sched.h
@@ -1327,6 +1327,13 @@ static inline int set_cpus_allowed(struc
#endif
extern unsigned long long sched_clock(void);
+
+/*
+ * For kernel-internal use: high-speed (but slightly incorrect) per-cpu
+ * clock constructed from sched_clock():
+ */
+extern unsigned long long cpu_clock(int cpu);
+
extern unsigned long long
task_sched_runtime(struct task_struct *task);
Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c
+++ linux/kernel/sched.c
@@ -365,6 +365,23 @@ static inline unsigned long long rq_cloc
}
/*
+ * For kernel-internal use: high-speed (but slightly incorrect) per-cpu
+ * clock constructed from sched_clock():
+ */
+unsigned long long cpu_clock(int cpu)
+{
+ struct rq *rq = cpu_rq(cpu);
+ unsigned long long now;
+ unsigned long flags;
+
+ spin_lock_irqsave(&rq->lock, flags);
+ now = rq_clock(rq);
+ spin_unlock_irqrestore(&rq->lock, flags);
+
+ return now;
+}
+
+/*
* The domain tree (rq->sd) is protected by RCU's quiescent state transition.
* See detach_destroy_domains: synchronize_sched for details.
*
Index: linux/kernel/softlockup.c
===================================================================
--- linux.orig/kernel/softlockup.c
+++ linux/kernel/softlockup.c
@@ -41,14 +41,16 @@ static struct notifier_block panic_block
* resolution, and we don't need to waste time with a big divide when
* 2^30ns == 1.074s.
*/
-static unsigned long get_timestamp(void)
+static unsigned long get_timestamp(int this_cpu)
{
- return sched_clock() >> 30; /* 2^30 ~= 10^9 */
+ return cpu_clock(this_cpu) >> 30; /* 2^30 ~= 10^9 */
}
void touch_softlockup_watchdog(void)
{
- __raw_get_cpu_var(touch_timestamp) = get_timestamp();
+ int this_cpu = raw_smp_processor_id();
+
+ per_cpu(touch_timestamp, this_cpu) = get_timestamp(this_cpu);
}
EXPORT_SYMBOL(touch_softlockup_watchdog);
@@ -94,7 +96,7 @@ void softlockup_tick(void)
return;
}
- now = get_timestamp();
+ now = get_timestamp(this_cpu);
/* Wake up the high-prio watchdog task every second: */
if (now > (touch_timestamp + 1))
-
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