From: Willy Tarreau <w@1wt.eu>
Date: Mon, 6 Jan 2025 17:55:48 +0000 (+0100)
Subject: MINOR: cpu-topo: fall back to nominal_perf and scaling_max_freq for the capacity
X-Git-Tag: v3.2-dev8~67
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d11241b7ba936ff823016cd2e6096822af58a46f;p=thirdparty%2Fhaproxy.git

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

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.
---

diff --git a/src/cpu_topo.c b/src/cpu_topo.c
index d93940895..47a97aea6 100644
--- a/src/cpu_topo.c
+++ b/src/cpu_topo.c
@@ -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 */