linux-kernel - Re: [PATCH] scheduler: fix x86 regression in native_sched

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Date:	Fri, 7 Dec 2007 10:59:31 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Guillaume Chazarain <guichaz@...oo.fr>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Stefano Brivio <stefano.brivio@...imi.it>,
	Robert Love <rml@...h9.net>, linux-kernel@...r.kernel.org,
	Dave Jones <davej@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Michael Buesch <mb@...sch.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] scheduler: fix x86 regression in native_sched_clock


* Guillaume Chazarain <guichaz@...oo.fr> wrote:

> I'll clean it up and resend it later. As I don't have the necessary 
> knowledge to do the tsc_{32,64}.c unification, should I copy paste 
> common functions into tsc_32.c and tsc_64.c to ease later unification 
> or should I start a common .c file?

note that there are a couple of existing patches in this area. One is 
the fix below. There's also older frequency-scaling TSC patches - i'll 
try to dig them out.

	Ingo

---------------->
Subject: x86: idle wakeup event in the HLT loop
From: Ingo Molnar <mingo@...e.hu>

do a proper idle-wakeup event on HLT as well - some CPUs stop the TSC
in HLT too, not just when going through the ACPI methods.

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/kernel/process_32.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

Index: linux/arch/x86/kernel/process_32.c
===================================================================
--- linux.orig/arch/x86/kernel/process_32.c
+++ linux/arch/x86/kernel/process_32.c
@@ -113,10 +113,19 @@ void default_idle(void)
 		smp_mb();
 
 		local_irq_disable();
-		if (!need_resched())
+		if (!need_resched()) {
+			ktime_t t0, t1;
+			u64 t0n, t1n;
+
+			t0 = ktime_get();
+			t0n = ktime_to_ns(t0);
 			safe_halt();	/* enables interrupts racelessly */
-		else
-			local_irq_enable();
+			local_irq_disable();
+			t1 = ktime_get();
+			t1n = ktime_to_ns(t1);
+			sched_clock_idle_wakeup_event(t1n - t0n);
+		}
+		local_irq_enable();
 		current_thread_info()->status |= TS_POLLING;
 	} else {
 		/* loop is done by the caller */
--
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