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MINOR: cpu-topo: fall back to nominal_perf and scaling_max_freq for the capacity

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When cpu_capacity is not present, let's try to check acpi_cppc's
nominal_perf which is similar and commonly found on servers, then
scaling_max_freq (though that last one may vary a bit between CPUs
depending on die quality). That variation is not a problem since
we can absorb a ~5% variation without issue.

It was verified on an i9-14900 featuring 5.7-P, 6.0-P and 4.4-E GHz
that P-cores were not reordered and that E cores were placed last.
It was also OK on a W3-2345 with 4.3 to 4.5GHz.
This commit is contained in:
Willy Tarreau 2025-01-06 18:55:48 +01:00
parent 322c28cc19
commit d11241b7ba
1 changed files with 24 additions and 0 deletions
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24
src/cpu_topo.c
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@ -406,6 +406,30 @@ int cpu_detect_topology(void)
if (trash.data)
ha_cpu_topo[cpu].capa = str2uic(trash.area);
}
/* When cpu_capacity is not available, sometimes acpi_cppc is
* available on servers to provide an equivalent metric allowing
* to distinguish big from small cores. Values as low as 15 and
* as high as 260 were seen there. Note that only nominal_perf
* is trustable, as nominal_freq may return zero. It's also
* more reliable than the max cpufreq values because it doesn't
* seem to take into account the die quality.
*/
if (ha_cpu_topo[cpu].capa < 0 &&
read_line_to_trash(NUMA_DETECT_SYSTEM_SYSFS_PATH "/cpu/cpu%d/acpi_cppc/nominal_perf", cpu) >= 0) {
if (trash.data)
ha_cpu_topo[cpu].capa = str2uic(trash.area);
}
/* Finally if none of them is available we can have a look at
* cpufreq's max cpu frequency.
*/
if (ha_cpu_topo[cpu].capa < 0 &&
read_line_to_trash(NUMA_DETECT_SYSTEM_SYSFS_PATH "/cpu/cpu%d/cpufreq/scaling_max_freq", cpu) >= 0) {
/* This is in kHz turn it to MHz to stay below 32k */
if (trash.data)
ha_cpu_topo[cpu].capa = (str2uic(trash.area) + 999U) / 1000U;
}
}
/* Now locate NUMA node IDs if any */