linux-kernel - [PATCH] x86: Fix call to set_cyc2ns_scale() from time_cpufreq

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Date:	Mon, 7 Apr 2008 12:14:45 +0200
From:	Karsten Wiese <fzu@...gehoertderstaat.de>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] x86: Fix call to set_cyc2ns_scale() from time_cpufreq_notifier()


In time_cpufreq_notifier() the cpu id to act upon is held in freq->cpu. Use it
instead of smp_processor_id() in the call to set_cyc2ns_scale().
This makes the preempt_*able() unnecessary and lets set_cyc2ns_scale() update
the intended cpu's cyc2ns.

Signed-off-by: Karsten Wiese <fzu@...gehoertderstaat.de>
---

Hi,

the codepath changed by patch is untested as my smp's cpu has
X86_FEATURE_CONSTANT_TSC set.
A printk() inserted at the beginning of time_cpufreq_notifier() showed regular
cases of "smp_processor_id() != freq->cpu".

Related mail/thread: http://lkml.org/lkml/2007/12/7/130.

Thanks,
      Karsten

 arch/x86/kernel/tsc_32.c |    4 +---
 arch/x86/kernel/tsc_64.c |    4 +---
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/tsc_32.c b/arch/x86/kernel/tsc_32.c
index d7498b3..2f5f9a4 100644
--- a/arch/x86/kernel/tsc_32.c
+++ b/arch/x86/kernel/tsc_32.c
@@ -256,9 +256,7 @@ time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data)
 						ref_freq, freq->new);
 			if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
 				tsc_khz = cpu_khz;
-				preempt_disable();
-				set_cyc2ns_scale(cpu_khz, smp_processor_id());
-				preempt_enable();
+				set_cyc2ns_scale(cpu_khz, freq->cpu);
 				/*
 				 * TSC based sched_clock turns
 				 * to junk w/ cpufreq
diff --git a/arch/x86/kernel/tsc_64.c b/arch/x86/kernel/tsc_64.c
index 01fc9f0..bd2e2c3 100644
--- a/arch/x86/kernel/tsc_64.c
+++ b/arch/x86/kernel/tsc_64.c
@@ -149,9 +149,7 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
 			mark_tsc_unstable("cpufreq changes");
 	}
 
-	preempt_disable();
-	set_cyc2ns_scale(tsc_khz_ref, smp_processor_id());
-	preempt_enable();
+	set_cyc2ns_scale(tsc_khz_ref, freq->cpu);
 
 	return 0;
 }
-- 
1.5.3.3
--
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