From 51d211e9c334b9eca3505f4052afa660c3e0606b Mon Sep 17 00:00:00 2001 From: Doug Smythies Date: Tue, 17 Jun 2014 13:36:10 -0700 Subject: intel_pstate: Correct rounding in busy calculation There was a mistake in the actual rounding portion this previous patch: f0fe3cd7e12d (intel_pstate: Correct rounding in busy calculation) such that the rounding was asymetric and incorrect. Severity: Not very serious, but can increase target pstate by one extra value. For real world work flows the issue should self correct (but I have no proof). It is the equivalent of different PID gains for positive and negative numbers. Examples: -3.000000 used to round to -4, rounds to -3 with this patch. -3.503906 used to round to -5, rounds to -4 with this patch. Fixes: f0fe3cd7e12d (intel_pstate: Correct rounding in busy calculation) Signed-off-by: Doug Smythies Cc: 3.14+ # 3.14+ Signed-off-by: Rafael J. Wysocki --- drivers/cpufreq/intel_pstate.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) (limited to 'drivers') diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c index 4e7f492ad583..924bb2d42b1c 100644 --- a/drivers/cpufreq/intel_pstate.c +++ b/drivers/cpufreq/intel_pstate.c @@ -196,10 +196,7 @@ static signed int pid_calc(struct _pid *pid, int32_t busy) pid->last_err = fp_error; result = pterm + mul_fp(pid->integral, pid->i_gain) + dterm; - if (result >= 0) - result = result + (1 << (FRAC_BITS-1)); - else - result = result - (1 << (FRAC_BITS-1)); + result = result + (1 << (FRAC_BITS-1)); return (signed int)fp_toint(result); } -- cgit v1.2.3