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util/cpu: add big.LITTLE cpu detection

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it's useful for drivers to be able to detect big.LITTLE topology in
order to make decisions about how to handle workloads (specifically as
it relates to threading)

Reviewed-by: Rob Clark <robdclark@chromium.org>

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21926>
This commit is contained in:
Mike Blumenkrantz 2023-03-15 10:26:13 -04:00 • committed by Marge Bot
parent 54d01db8a8
commit 0cc93a4603
2 changed files with 46 additions and 0 deletions
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35
src/util/u_cpu_detect.c
View file

@ -38,6 +38,7 @@
#include "util/u_debug.h"
#include "u_cpu_detect.h"
#include "u_math.h"
#include "os_file.h"
#include "c11/threads.h"
#include <stdio.h>
@ -478,6 +479,40 @@ get_cpu_topology(void)
memset(util_cpu_caps.cpu_to_L3, 0xff, sizeof(util_cpu_caps.cpu_to_L3));
#if DETECT_OS_LINUX
uint64_t big_cap = 0;
unsigned num_big_cpus = 0;
uint64_t *caps = malloc(sizeof(uint64_t) * util_cpu_caps.max_cpus);
bool fail = false;
for (unsigned i = 0; caps && i < util_cpu_caps.max_cpus; i++) {
char name[PATH_MAX];
snprintf(name, sizeof(name), "/sys/devices/system/cpu/cpu%u/cpu_capacity", i);
size_t size = 0;
char *cap = os_read_file(name, &size);
if (!cap) {
num_big_cpus = 0;
fail = true;
break;
}
errno = 0;
caps[i] = strtoull(cap, NULL, 10);
free(cap);
if (errno) {
fail = true;
break;
}
big_cap = MAX2(caps[i], big_cap);
}
if (!fail) {
for (unsigned i = 0; caps && i < util_cpu_caps.max_cpus; i++) {
if (caps[i] >= big_cap / 2)
num_big_cpus++;
}
}
free(caps);
util_cpu_caps.nr_big_cpus = num_big_cpus;
#endif
#if DETECT_ARCH_X86 || DETECT_ARCH_X86_64
/* AMD Zen */
if (util_cpu_caps.family >= CPU_AMD_ZEN1_ZEN2 &&

11
src/util/u_cpu_detect.h
View file

@ -126,8 +126,19 @@ struct util_cpu_caps_t {
unsigned max_vector_bits;
uint16_t cpu_to_L3[UTIL_MAX_CPUS];
/* Affinity masks for each L3 cache. */
util_affinity_mask *L3_affinity_mask;
/**
* number of "big" CPUs in big.LITTLE configuration
*
* a "big" CPU is defined as anything with >= 50% the capacity of the largest CPU,
* useful for drivers determining how many and what kinds of threads to use
* example: 1x prime + 3x big + 4x little = 4x "big" cores
*
* A value of zero indicates that CPUs are homogeneous.
*/
int16_t nr_big_cpus;
};
struct _util_cpu_caps_state_t {