qemu/hw/core/machine-smp.c
Yanan Wang 864c3b5c32 hw/core/machine: Introduce CPU cluster topology support
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>
2021-12-31 13:42:39 +01:00

196 lines
7.3 KiB
C

/*
* QEMU Machine core (related to -smp parsing)
*
* Copyright (c) 2021 Huawei Technologies Co., Ltd
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License,
* or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include "qemu/osdep.h"
#include "hw/boards.h"
#include "qapi/error.h"
/*
* Report information of a machine's supported CPU topology hierarchy.
* Topology members will be ordered from the largest to the smallest
* in the string.
*/
static char *cpu_hierarchy_to_string(MachineState *ms)
{
MachineClass *mc = MACHINE_GET_CLASS(ms);
GString *s = g_string_new(NULL);
g_string_append_printf(s, "sockets (%u)", ms->smp.sockets);
if (mc->smp_props.dies_supported) {
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);
return g_string_free(s, false);
}
/*
* machine_parse_smp_config: Generic function used to parse the given
* SMP configuration
*
* Any missing parameter in "cpus/maxcpus/sockets/cores/threads" will be
* automatically computed based on the provided ones.
*
* In the calculation of omitted sockets/cores/threads: we prefer sockets
* over cores over threads before 6.2, while preferring cores over sockets
* over threads since 6.2.
*
* In the calculation of cpus/maxcpus: When both maxcpus and cpus are omitted,
* maxcpus will be computed from the given parameters and cpus will be set
* equal to maxcpus. When only one of maxcpus and cpus is given then the
* omitted one will be set to its given counterpart's value. Both maxcpus and
* cpus may be specified, but maxcpus must be equal to or greater than cpus.
*
* For compatibility, apart from the parameters that will be computed, newly
* introduced topology members which are likely to be target specific should
* be directly set as 1 if they are omitted (e.g. dies for PC since 4.1).
*/
void machine_parse_smp_config(MachineState *ms,
const SMPConfiguration *config, Error **errp)
{
MachineClass *mc = MACHINE_GET_CLASS(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;
/*
* Specified CPU topology parameters must be greater than zero,
* explicit configuration like "cpus=0" is not allowed.
*/
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)) {
warn_report("Deprecated CPU topology (considered invalid): "
"CPU topology parameters must be greater than zero");
}
/*
* If not supported by the machine, a topology parameter must be
* omitted or specified equal to 1.
*/
if (!mc->smp_props.dies_supported && dies > 1) {
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) {
sockets = sockets > 0 ? sockets : 1;
cores = cores > 0 ? cores : 1;
threads = threads > 0 ? threads : 1;
} else {
maxcpus = maxcpus > 0 ? maxcpus : cpus;
if (mc->smp_props.prefer_sockets) {
/* prefer sockets over cores before 6.2 */
if (sockets == 0) {
cores = cores > 0 ? cores : 1;
threads = threads > 0 ? threads : 1;
sockets = maxcpus / (dies * clusters * cores * threads);
} else if (cores == 0) {
threads = threads > 0 ? threads : 1;
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 * clusters * threads);
} else if (sockets == 0) {
threads = threads > 0 ? threads : 1;
sockets = maxcpus / (dies * clusters * cores * threads);
}
}
/* try to calculate omitted threads at last */
if (threads == 0) {
threads = maxcpus / (sockets * dies * clusters * cores);
}
}
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 * 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: "
"%s != maxcpus (%u)",
topo_msg, maxcpus);
return;
}
if (maxcpus < cpus) {
g_autofree char *topo_msg = cpu_hierarchy_to_string(ms);
error_setg(errp, "Invalid CPU topology: "
"maxcpus must be equal to or greater than smp: "
"%s == maxcpus (%u) < smp_cpus (%u)",
topo_msg, maxcpus, cpus);
return;
}
if (ms->smp.cpus < mc->min_cpus) {
error_setg(errp, "Invalid SMP CPUs %d. The min CPUs "
"supported by machine '%s' is %d",
ms->smp.cpus,
mc->name, mc->min_cpus);
return;
}
if (ms->smp.max_cpus > mc->max_cpus) {
error_setg(errp, "Invalid SMP CPUs %d. The max CPUs "
"supported by machine '%s' is %d",
ms->smp.max_cpus,
mc->name, mc->max_cpus);
return;
}
}