Re: [patch] fix the softlockup watchdog to actually work

[Ingo Molnar <mingo@elte.hu>]

* Andrew Morton <akpm@linux-foundation.org> wrote:

> >   * 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);
> >  
> > @@ -95,7 +97,7 @@ void softlockup_tick(void)
> >  		return;
> 
> argh.  afacit this was never sent, except as part of some jumbopatch 
> called "sched: implement cpu_clock(cpu) high-speed time source".
> 
> That patch helped.
> 
> It's all a plot.

sorry, it's really my fault: i decoupled it from the jumbopatch (so that 
the new API could go in first) but forgot to re-send that crutial bit. 
There's also the patch below (Jens Cc:-ed) to update blktrace. I guess i 
should do a softlockup.git tree to avoid such foul-ups in the future.

	Ingo

----------------------->
Subject: blktrace: use cpu_clock() instead of sched_clock()
From: Ingo Molnar <mingo@elte.hu>

use cpu_clock() instead of sched_clock(). (the latter is not a proper
clock-source)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 block/blktrace.c |   20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 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();
 }