This is a note to let you know that I've just added the patch titled
cpufreq: intel_pstate: Fix divide by zero on Knights Landing (KNL)
to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cpufreq-intel_pstate-fix-divide-by-zero-on-knights-landing-knl.patch
and it can be found in the queue-4.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 8e601a9f97a00bab031980de34f9a81891c1f82f Mon Sep 17 00:00:00 2001
From: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Date: Thu, 15 Oct 2015 12:34:21 -0700
Subject: cpufreq: intel_pstate: Fix divide by zero on Knights Landing (KNL)
From: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
commit 8e601a9f97a00bab031980de34f9a81891c1f82f upstream.
This is a workaround for KNL platform, where in some cases MPERF counter
will not have updated value before next read of MSR_IA32_MPERF. In this
case divide by zero will occur. This change ignores current sample for
busy calculation in this case.
Fixes: b34ef932d79a (intel_pstate: Knights Landing support)
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Acked-by: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/cpufreq/intel_pstate.c | 5 +++++
1 file changed, 5 insertions(+)
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -761,6 +761,11 @@ static inline void intel_pstate_sample(s
local_irq_save(flags);
rdmsrl(MSR_IA32_APERF, aperf);
rdmsrl(MSR_IA32_MPERF, mperf);
+ if (cpu->prev_mperf == mperf) {
+ local_irq_restore(flags);
+ return;
+ }
+
local_irq_restore(flags);
cpu->last_sample_time = cpu->sample.time;
Patches currently in stable-queue which might be from srinivas.pandruvada@xxxxxxxxxxxxxxx are
queue-4.1/cpufreq-intel_pstate-fix-divide-by-zero-on-knights-landing-knl.patch
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