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intel_pstate: Correct rounding in busy calculation 

There was a mistake in the actual rounding portion this previous patch:
f0fe3cd7e1 (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: f0fe3cd7e1 (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>
This commit is contained in:
Doug Smythies 2014-06-17 13:36:10 -07:00 committed by Rafael J. Wysocki
parent 217886d3f3
commit 51d211e9c3
1 changed files with 1 additions and 4 deletions
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5
drivers/cpufreq/intel_pstate.c
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@ -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);
}