linux-kernel - [PATCH] cpufreq: intel_pstate: Fix rounding of core

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Date:	Wed, 11 Jun 2014 15:33:32 +0300
From:	Stratos Karafotis <stratosk@...aphore.gr>
To:	rjw@...ysocki.net, viresh.kumar@...aro.org,
	dirk.j.brandewie@...el.com
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] cpufreq: intel_pstate: Fix rounding of core_pct

Local variable core_pct holds fixed point values.
When we round it we add "1" to core_pct. This has almost
no effect.

So, add int_toftp(1) to core_pct when rounding.

For example, in a given sample point (values taken from
tracepoint) with:
aperf = 5024
mperf = 10619

the core_pct is (before rounding):
core_pct = 12111
fp_toint(core_pct) = 47

After rounding:
core_pct = 12112
fp_toint(core_pct) = 47

After rounding with int_toftp(1):
core_pct = 12367
fp_toint(core_pct) = 48

Signed-off-by: Stratos Karafotis <stratosk@...aphore.gr>
---

Hi Rafael,

I'm sorry for submitting again in merge window, but
I thought that maybe we need this fix for 3.16.


 drivers/cpufreq/intel_pstate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 4e7f492..dd80aa2 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -564,7 +564,7 @@ static inline void intel_pstate_calc_busy(struct cpudata *cpu)
 	core_pct = div_u64_rem(core_pct, int_tofp(sample->mperf), &rem);
 
 	if ((rem << 1) >= int_tofp(sample->mperf))
-		core_pct += 1;
+		core_pct += int_tofp(1);
 
 	sample->freq = fp_toint(
 		mul_fp(int_tofp(cpu->pstate.max_pstate * 1000), core_pct));
-- 
1.9.3

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