* Christian Borntraeger <borntraeger@de.ibm.com> wrote:

quoted text
> Am Montag, 20. August 2007 schrieb Ingo Molnar:
> > could you send that precise sched_clock() patch? It should be an order 
> > of magnitude simpler than the high-precision stime/utime tracking you 
> > already do, and it's needed for quality scheduling anyway.
> 
> I have a question about that. I just played with sched_clock, and even 
> when I intentionally slow down sched_clock by a factor of 2, my cpu 
> bound process gets 100 % in top. If this is intentional, I dont 
> understand how a virtualized sched_clock would fix the accounting 
> change?

could you try the patch below, does it work any better?

	Ingo

---
 kernel/sched.c |    9 +++++++++
 1 file changed, 9 insertions(+)

Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c
+++ linux/kernel/sched.c
@@ -333,6 +333,14 @@ static void __update_rq_clock(struct rq 
 #ifdef CONFIG_SCHED_DEBUG
 	WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());
 #endif
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+	/*
+	 * Trust sched_clock on s390:
+	 */
+	if (unlikely(delta > rq->clock_max_delta))
+		rq->clock_max_delta = delta;
+	clock += delta;
+#else
 	/*
 	 * Protect against sched_clock() occasionally going backwards:
 	 */
@@ -355,6 +363,7 @@ static void __update_rq_clock(struct rq 
 			clock += delta;
 		}
 	}
+#endif
 
 	rq->prev_clock_raw = now;
 	rq->clock = clock;
-
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