From: Doug Smythies Date: Tue, 17 Jun 2014 20:36:10 +0000 (-0700) Subject: intel_pstate: Correct rounding in busy calculation X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=f4e368a53c65f8acd462b2b038c18a21d30eaeb8;p=karo-tx-linux.git intel_pstate: Correct rounding in busy calculation commit 51d211e9c334b9eca3505f4052afa660c3e0606b upstream. 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 Signed-off-by: Rafael J. Wysocki Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c index de9ef4a1986d..6d98c37c87ad 100644 --- a/drivers/cpufreq/intel_pstate.c +++ b/drivers/cpufreq/intel_pstate.c @@ -200,10 +200,7 @@ 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); }