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hw/core/machine: Introduce CPU cluster topology support

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The new Cluster-Aware Scheduling support has landed in Linux 5.16,
which has been proved to benefit the scheduling performance (e.g.
load balance and wake_affine strategy) on both x86_64 and AArch64.

So now in Linux 5.16 we have four-level arch-neutral CPU topology
definition like below and a new scheduler level for clusters.
struct cpu_topology {
    int thread_id;
    int core_id;
    int cluster_id;
    int package_id;
    int llc_id;
    cpumask_t thread_sibling;
    cpumask_t core_sibling;
    cpumask_t cluster_sibling;
    cpumask_t llc_sibling;
}

A cluster generally means a group of CPU cores which share L2 cache
or other mid-level resources, and it is the shared resources that
is used to improve scheduler's behavior. From the point of view of
the size range, it's between CPU die and CPU core. For example, on
some ARM64 Kunpeng servers, we have 6 clusters in each NUMA node,
and 4 CPU cores in each cluster. The 4 CPU cores share a separate
L2 cache and a L3 cache tag, which brings cache affinity advantage.

In virtualization, on the Hosts which have pClusters (physical
clusters), if we can design a vCPU topology with cluster level for
guest kernel and have a dedicated vCPU pinning. A Cluster-Aware
Guest kernel can also make use of the cache affinity of CPU clusters
to gain similar scheduling performance.

This patch adds infrastructure for CPU cluster level topology
configuration and parsing, so that the user can specify cluster
parameter if their machines support it.

Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
Message-Id: <20211228092221.21068-3-wangyanan55@huawei.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
[PMD: Added '(since 7.0)' to @clusters in qapi/machine.json]
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
This commit is contained in:
Yanan Wang 2021-12-28 17:22:09 +08:00 • committed by Philippe Mathieu-Daudé
parent 0d87178523
commit 864c3b5c32
6 changed files with 38 additions and 12 deletions
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26
hw/core/machine-smp.c
View file

@ -37,6 +37,10 @@ static char *cpu_hierarchy_to_string(MachineState *ms)
g_string_append_printf(s, " * dies (%u)", ms->smp.dies);
}
if (mc->smp_props.clusters_supported) {
g_string_append_printf(s, " * clusters (%u)", ms->smp.clusters);
}
g_string_append_printf(s, " * cores (%u)", ms->smp.cores);
g_string_append_printf(s, " * threads (%u)", ms->smp.threads);
@ -71,6 +75,7 @@ void machine_parse_smp_config(MachineState *ms,
unsigned cpus = config->has_cpus ? config->cpus : 0;
unsigned sockets = config->has_sockets ? config->sockets : 0;
unsigned dies = config->has_dies ? config->dies : 0;
unsigned clusters = config->has_clusters ? config->clusters : 0;
unsigned cores = config->has_cores ? config->cores : 0;
unsigned threads = config->has_threads ? config->threads : 0;
unsigned maxcpus = config->has_maxcpus ? config->maxcpus : 0;
@ -82,6 +87,7 @@ void machine_parse_smp_config(MachineState *ms,
if ((config->has_cpus && config->cpus == 0) ||
(config->has_sockets && config->sockets == 0) ||
(config->has_dies && config->dies == 0) ||
(config->has_clusters && config->clusters == 0) ||
(config->has_cores && config->cores == 0) ||
(config->has_threads && config->threads == 0) ||
(config->has_maxcpus && config->maxcpus == 0)) {
@ -97,8 +103,13 @@ void machine_parse_smp_config(MachineState *ms,
error_setg(errp, "dies not supported by this machine's CPU topology");
return;
}
if (!mc->smp_props.clusters_supported && clusters > 1) {
error_setg(errp, "clusters not supported by this machine's CPU topology");
return;
}
dies = dies > 0 ? dies : 1;
clusters = clusters > 0 ? clusters : 1;
/* compute missing values based on the provided ones */
if (cpus == 0 && maxcpus == 0) {
@ -113,41 +124,42 @@ void machine_parse_smp_config(MachineState *ms,
if (sockets == 0) {
cores = cores > 0 ? cores : 1;
threads = threads > 0 ? threads : 1;
sockets = maxcpus / (dies * cores * threads);
sockets = maxcpus / (dies * clusters * cores * threads);
} else if (cores == 0) {
threads = threads > 0 ? threads : 1;
cores = maxcpus / (sockets * dies * threads);
cores = maxcpus / (sockets * dies * clusters * threads);
}
} else {
/* prefer cores over sockets since 6.2 */
if (cores == 0) {
sockets = sockets > 0 ? sockets : 1;
threads = threads > 0 ? threads : 1;
cores = maxcpus / (sockets * dies * threads);
cores = maxcpus / (sockets * dies * clusters * threads);
} else if (sockets == 0) {
threads = threads > 0 ? threads : 1;
sockets = maxcpus / (dies * cores * threads);
sockets = maxcpus / (dies * clusters * cores * threads);
}
}
/* try to calculate omitted threads at last */
if (threads == 0) {
threads = maxcpus / (sockets * dies * cores);
threads = maxcpus / (sockets * dies * clusters * cores);
}
}
maxcpus = maxcpus > 0 ? maxcpus : sockets * dies * cores * threads;
maxcpus = maxcpus > 0 ? maxcpus : sockets * dies * clusters * cores * threads;
cpus = cpus > 0 ? cpus : maxcpus;
ms->smp.cpus = cpus;
ms->smp.sockets = sockets;
ms->smp.dies = dies;
ms->smp.clusters = clusters;
ms->smp.cores = cores;
ms->smp.threads = threads;
ms->smp.max_cpus = maxcpus;
/* sanity-check of the computed topology */
if (sockets * dies * cores * threads != maxcpus) {
if (sockets * dies * clusters * cores * threads != maxcpus) {
g_autofree char *topo_msg = cpu_hierarchy_to_string(ms);
error_setg(errp, "Invalid CPU topology: "
"product of the hierarchy must match maxcpus: "