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| author | Oleg Keri <okerixx@gmail.com> | 2026-09-23 14:56:04 +0200 |
|---|---|---|
| committer | Will Deacon <will@kernel.org> | 2026-09-24 09:20:31 +0000 |
| commit | 3872cc6b92940af0f73c6f9a45d65300492d648d (patch) | |
| tree | 52b06c34940d0cb36a3e4d65f44d2c40e53ff72a /arch | |
| parent | 1fef81669147d63eb8c5d3627d54eadc21173a0b (diff) | |
| download | linux-stable-3872cc6b92940af0f73c6f9a45d65300492d648d.tar.gz linux-stable-3872cc6b92940af0f73c6f9a45d65300492d648d.zip | |
arm64: topology: fix arch_freq_get_on_cpu() overflow above 4.19 GHz
arch_freq_get_on_cpu() computes the product of the frequency scale and
the reference frequency as a u64, but assigns it to an unsigned int
before shifting it back down:
freq = scale * arch_scale_freq_ref(cpu);
freq >>= SCHED_CAPACITY_SHIFT;
The product is truncated to 32 bits before the shift, so the result
wraps once arch_scale_freq_ref() exceeds 2^32 / SCHED_CAPACITY_SCALE,
i.e. 4194304 kHz.
On a Snapdragon X2 Elite (Glymur) laptop, whose boost OPP is 4723200
kHz, cpuinfo_avg_freq reports 524283 kHz instead of ~4723200 kHz while
the CPU demonstrably runs at the boost frequency: a fixed workload
completes in 1.72 s at the 4723200 kHz OPP versus 2.01 s at 4032000
kHz, matching the 1.171 frequency ratio.
Shift the u64 product and narrow only at the return.
Fixes: 16d1e27475f6 ("arm64: Provide an AMU-based version of arch_freq_get_on_cpu")
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Oleg Keri <okerixx@gmail.com>
Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/arm64/kernel/topology.c | 6 |
1 files changed, 2 insertions, 4 deletions
diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c index d28438f8b..1773dac6f 100644 --- a/arch/arm64/kernel/topology.c +++ b/arch/arm64/kernel/topology.c @@ -186,7 +186,6 @@ int arch_freq_get_on_cpu(int cpu) struct amu_cntr_sample *amu_sample; unsigned int start_cpu = cpu; unsigned long last_update; - unsigned int freq = 0; u64 scale; if (!amu_fie_cpu_supported(cpu) || !arch_scale_freq_ref(cpu)) @@ -245,9 +244,8 @@ int arch_freq_get_on_cpu(int cpu) * (see amu_scale_freq_tick for details) */ scale = arch_scale_freq_capacity(cpu); - freq = scale * arch_scale_freq_ref(cpu); - freq >>= SCHED_CAPACITY_SHIFT; - return freq; + + return (scale * arch_scale_freq_ref(cpu)) >> SCHED_CAPACITY_SHIFT; } static void amu_fie_setup(const struct cpumask *cpus) |