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Date: Wed, 22 Jan 2014 22:08:14 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Markus Trippelsdorf <markus@trippelsdorf.de>
Cc: Sasha Levin <sasha.levin@oracle.com>,
Arjan van de Ven <arjan@linux.intel.com>, lenb@kernel.org,
rjw@rjwysocki.net, Eliezer Tamir <eliezer.tamir@linux.intel.com>,
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John Stultz <john.stultz@linaro.org>,
Andy Lutomirski <luto@amacapital.net>,
linux-kernel@vger.kernel.org, dyoung@redhat.com
Subject: Re: [PATCH 13/15] sched: Use a static_key for sched_clock_stable
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>
> I think its the right region to look through. My current suspect is the
> linear continuity fit with the initial 'random' multiplier.
>
> That initial 'random' multiplier can get us quite high, and we'll fit
> the function to match that but continue at a sane rate.
>
> I'll try and prod a little more later this evening as time permits.
Does this cure things?
---
arch/x86/kernel/tsc.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index a3acbac2ee72..bb04148c5fe0 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -237,7 +237,7 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
/* XXX surely we already have this someplace in the kernel?! */
#define DIV_ROUND(n, d) (((n) + ((d) / 2)) / (d))
-static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
+static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu, bool origin)
{
unsigned long long tsc_now, ns_now;
struct cyc2ns_data *data;
@@ -252,7 +252,10 @@ static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
data = cyc2ns_write_begin(cpu);
rdtscll(tsc_now);
- ns_now = cycles_2_ns(tsc_now);
+ if (origin)
+ ns_now = 0;
+ else
+ ns_now = cycles_2_ns(tsc_now);
/*
* Compute a new multiplier as per the above comment and ensure our
@@ -926,7 +929,7 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
mark_tsc_unstable("cpufreq changes");
}
- set_cyc2ns_scale(tsc_khz, freq->cpu);
+ set_cyc2ns_scale(tsc_khz, freq->cpu, false);
return 0;
}
@@ -1199,7 +1202,7 @@ void __init tsc_init(void)
*/
for_each_possible_cpu(cpu) {
cyc2ns_init(cpu);
- set_cyc2ns_scale(cpu_khz, cpu);
+ set_cyc2ns_scale(cpu_khz, cpu, true);
}
if (tsc_disabled > 0)
--
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