linux-kernel - Re: CONFIG_NO_HZ breaks blktrace timestamps

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Message-ID: <20080111095121.GG8143@elte.hu>
Date:	Fri, 11 Jan 2008 10:51:24 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	David Dillow <dillowda@...l.gov>
Cc:	Guillaume Chazarain <guichaz@...oo.fr>,
	linux-kernel@...r.kernel.org, linux-btrace@...r.kernel.org,
	mingo@...hat.com, tglx@...utronix.de
Subject: Re: CONFIG_NO_HZ breaks blktrace timestamps


* Ingo Molnar <mingo@...e.hu> wrote:

> > With those patches, CONFIG_NO_HZ works just fine.
> 
> could you please try the two patches below, do they fix the problem as 
> well? They got a ton of testing in x86.git in the past ~2 months and 
> we could perhaps still push them into v2.6.24.

plus, if needed, perhaps this patch below from Guillaume ontop of it.

	Ingo

---------------->
Subject: sched: fix rq->clock warps on frequency changes
From: Guillaume Chazarain <guichaz@...oo.fr>

sched: fix rq->clock warps on frequency changes

Fix 2bacec8c318ca0418c0ee9ac662ee44207765dd4
(sched: touch softlockup watchdog after idling) that reintroduced warps
on frequency changes. touch_softlockup_watchdog() calls __update_rq_clock
that checks rq->clock for warps, so call it after adjusting rq->clock.

Signed-off-by: Guillaume Chazarain <guichaz@...oo.fr>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-x86.q/kernel/sched.c
===================================================================
--- linux-x86.q.orig/kernel/sched.c
+++ linux-x86.q/kernel/sched.c
@@ -668,7 +668,6 @@ void sched_clock_idle_wakeup_event(u64 d
 	struct rq *rq = cpu_rq(smp_processor_id());
 	u64 now = sched_clock();
 
-	touch_softlockup_watchdog();
 	rq->idle_clock += delta_ns;
 	/*
 	 * Override the previous timestamp and ignore all
@@ -680,6 +679,7 @@ void sched_clock_idle_wakeup_event(u64 d
 	rq->prev_clock_raw = now;
 	rq->clock += delta_ns;
 	spin_unlock(&rq->lock);
+	touch_softlockup_watchdog();
 }
 EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
 
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