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| author | Doug Smythies <doug.smythies@gmail.com> | 2014-06-17 13:36:10 -0700 |
|---|---|---|
| committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2014-06-17 22:57:40 +0200 |
| commit | 51d211e9c334b9eca3505f4052afa660c3e0606b (patch) | |
| tree | f515484b6eb8f1f5b75bfaa3ec969747a3b41706 | |
| parent | 217886d3f3191f1f052e987740ee2bb32a4fd316 (diff) | |
| download | linux-51d211e9c334b9eca3505f4052afa660c3e0606b.tar.gz | |
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 <dsmythies@telus.net>
Cc: 3.14+ <stable@vger.kernel.org> # 3.14+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
| -rw-r--r-- | drivers/cpufreq/intel_pstate.c | 5 |
1 files changed, 1 insertions, 4 deletions
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c index 4e7f492ad5839d..924bb2d42b1c8c 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); } |