[PATCH] cpufreq: amd_freq_sensitivity: Fix sensitivity clamping in amd_powersave_bias_target
The local variable 'sensitivity' was never clamped to 0 or POWERSAVE_BIAS_MAX because the return value of clamp() was not used. Fix this by assigning the clamped value back to 'sensitivity'.
Cc: stable@vger.kernel.org Fixes: 9c5320c8ea8b ("cpufreq: AMD "frequency sensitivity feedback" powersave bias for ondemand governor") Signed-off-by: Thorsten Blum thorsten.blum@linux.dev --- drivers/cpufreq/amd_freq_sensitivity.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/cpufreq/amd_freq_sensitivity.c b/drivers/cpufreq/amd_freq_sensitivity.c index 13fed4b9e02b..713ccf24c97d 100644 --- a/drivers/cpufreq/amd_freq_sensitivity.c +++ b/drivers/cpufreq/amd_freq_sensitivity.c @@ -76,7 +76,7 @@ static unsigned int amd_powersave_bias_target(struct cpufreq_policy *policy, sensitivity = POWERSAVE_BIAS_MAX - (POWERSAVE_BIAS_MAX * (d_reference - d_actual) / d_reference);
- clamp(sensitivity, 0, POWERSAVE_BIAS_MAX); + sensitivity = clamp(sensitivity, 0, POWERSAVE_BIAS_MAX);
/* this workload is not CPU bound, so choose a lower freq */ if (sensitivity < od_tuners->powersave_bias) {
On 2. Dec 2025, at 20:09, David Laight wrote:
On Tue, 2 Dec 2025 13:44:28 +0100 Thorsten Blum thorsten.blum@linux.dev wrote:
The local variable 'sensitivity' was never clamped to 0 or POWERSAVE_BIAS_MAX because the return value of clamp() was not used. Fix this by assigning the clamped value back to 'sensitivity'.
This actually makes no difference (assuming od_tuners->powersave_bias <= POWERSAVE_BIAS_MAX). The only use of 'sensitivity' is the test at the end of the diff.
So I think you could just delete the line.
The local variable 'sensitivity' is an 'int', while '->powersave_bias' is an 'unsigned int'. If 'sensitivity' were ever negative, it would be converted to an 'unsigned int', producing an incorrect result. That's probably what the clamping was meant to prevent.
However, calculating 'sensitivity' can be simplified from:
sensitivity = POWERSAVE_BIAS_MAX - (POWERSAVE_BIAS_MAX * (d_reference - d_actual) / d_reference);
to:
sensitivity = POWERSAVE_BIAS_MAX * d_actual / d_reference;
which makes it clearer that, in practice, 'sensitivity' is never negative. How about simplifying the formula as above, changing 'sensitivity' to 'unsigned int', and removing the clamping?
Thanks, Thorsten
On 19. Dec 2025, at 16:55, Thorsten Blum wrote:
On 2. Dec 2025, at 20:09, David Laight wrote:
On Tue, 2 Dec 2025 13:44:28 +0100 Thorsten Blum thorsten.blum@linux.dev wrote:
The local variable 'sensitivity' was never clamped to 0 or POWERSAVE_BIAS_MAX because the return value of clamp() was not used. Fix this by assigning the clamped value back to 'sensitivity'.
This actually makes no difference (assuming od_tuners->powersave_bias <= POWERSAVE_BIAS_MAX). The only use of 'sensitivity' is the test at the end of the diff.
So I think you could just delete the line.
The local variable 'sensitivity' is an 'int', while '->powersave_bias' is an 'unsigned int'. If 'sensitivity' were ever negative, it would be converted to an 'unsigned int', producing an incorrect result. That's probably what the clamping was meant to prevent.
However, calculating 'sensitivity' can be simplified from:
sensitivity = POWERSAVE_BIAS_MAX - (POWERSAVE_BIAS_MAX * (d_reference - d_actual) / d_reference);
to:
sensitivity = POWERSAVE_BIAS_MAX * d_actual / d_reference;
which makes it clearer that, in practice, 'sensitivity' is never negative. How about simplifying the formula as above, changing 'sensitivity' to 'unsigned int', and removing the clamping?
Hm, changing the formula could alter the integer arithmetic, potentially producing slightly different results, and might even overflow.
I guess we should keep the formula as is and either defensively clamp 'sensitivity', as originally intended, or just remove the line (since this seems to have been working since 2013 and as suggested by David).
I'm slightly in favor of clamping the value because the assumptions aren't obvious to me.
Any preferences or other suggestions?
Thanks, Thorsten
On Tue, 2 Dec 2025 13:44:28 +0100 Thorsten Blum thorsten.blum@linux.dev wrote:
The local variable 'sensitivity' was never clamped to 0 or POWERSAVE_BIAS_MAX because the return value of clamp() was not used. Fix this by assigning the clamped value back to 'sensitivity'.
This actually makes no difference (assuming od_tuners->powersave_bias <= POWERSAVE_BIAS_MAX). The only use of 'sensitivity' is the test at the end of the diff.
So I think you could just delete the line.
David
Cc: stable@vger.kernel.org Fixes: 9c5320c8ea8b ("cpufreq: AMD "frequency sensitivity feedback" powersave bias for ondemand governor") Signed-off-by: Thorsten Blum thorsten.blum@linux.dev
drivers/cpufreq/amd_freq_sensitivity.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/cpufreq/amd_freq_sensitivity.c b/drivers/cpufreq/amd_freq_sensitivity.c index 13fed4b9e02b..713ccf24c97d 100644 --- a/drivers/cpufreq/amd_freq_sensitivity.c +++ b/drivers/cpufreq/amd_freq_sensitivity.c @@ -76,7 +76,7 @@ static unsigned int amd_powersave_bias_target(struct cpufreq_policy *policy, sensitivity = POWERSAVE_BIAS_MAX - (POWERSAVE_BIAS_MAX * (d_reference - d_actual) / d_reference);
- clamp(sensitivity, 0, POWERSAVE_BIAS_MAX);
- sensitivity = clamp(sensitivity, 0, POWERSAVE_BIAS_MAX);
/* this workload is not CPU bound, so choose a lower freq */ if (sensitivity < od_tuners->powersave_bias) {
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David Laight -
Thorsten Blum