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cpufreq: intel_pstate: Disable interrupts during MSRs reading

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According to Intel 64 and IA-32 Architectures SDM, Volume 3,
Chapter 14.2, "Software needs to exercise care to avoid delays
between the two RDMSRs (for example interrupts)".

So, disable interrupts during reading MSRs IA32_APERF and IA32_MPERF.
This should increase the accuracy of the calculations.

Signed-off-by: Stratos Karafotis <[email protected]>
Signed-off-by: Dirk Brandewie <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>
This commit is contained in:
Stratos Karafotis 2014-07-18 08:37:24 -07:00 • committed by Rafael J. Wysocki
commit 4ab60c3f32
1 changed files with 3 additions and 0 deletions
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3
drivers/cpufreq/intel_pstate.c
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@ -577,9 +577,12 @@ static inline void intel_pstate_calc_busy(struct cpudata *cpu)
static inline void intel_pstate_sample(struct cpudata *cpu)
{
u64 aperf, mperf;
unsigned long flags;
local_irq_save(flags);
rdmsrl(MSR_IA32_APERF, aperf);
rdmsrl(MSR_IA32_MPERF, mperf);
local_irq_restore(flags);
aperf = aperf >> FRAC_BITS;
mperf = mperf >> FRAC_BITS;