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machine: Prefer cores over sockets in smp parsing since 6.2

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In the real SMP hardware topology world, it's much more likely that
we have high cores-per-socket counts and few sockets totally. While
the current preference of sockets over cores in smp parsing results
in a virtual cpu topology with low cores-per-sockets counts and a
large number of sockets, which is just contrary to the real world.

Given that it is better to make the virtual cpu topology be more
reflective of the real world and also for the sake of compatibility,
we start to prefer cores over sockets over threads in smp parsing
since machine type 6.2 for different arches.

In this patch, a boolean "smp_prefer_sockets" is added, and we only
enable the old preference on older machines and enable the new one
since type 6.2 for all arches by using the machine compat mechanism.

Suggested-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta@ionos.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20210929025816.21076-10-wangyanan55@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Yanan Wang 2021-09-29 10:58:09 +08:00 committed by Paolo Bonzini
parent bbb0c0ec6d
commit 4a0af2930a
9 changed files with 60 additions and 19 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

1
hw/arm/virt.c
View file

@ -2815,6 +2815,7 @@ static void virt_machine_6_1_options(MachineClass *mc)
virt_machine_6_2_options(mc);
compat_props_add(mc->compat_props, hw_compat_6_1, hw_compat_6_1_len);
mc->smp_prefer_sockets = true;
/* qemu ITS was introduced with 6.2 */
vmc->no_tcg_its = true;

35
hw/core/machine.c
View file

@ -748,6 +748,7 @@ void machine_set_cpu_numa_node(MachineState *machine,
static void smp_parse(MachineState *ms, 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 cores = config->has_cores ? config->cores : 0;
@ -759,7 +760,7 @@ static void smp_parse(MachineState *ms, SMPConfiguration *config, Error **errp)
return;
}
/* compute missing values, prefer sockets over cores over threads */
/* compute missing values based on the provided ones */
if (cpus == 0 && maxcpus == 0) {
sockets = sockets > 0 ? sockets : 1;
cores = cores > 0 ? cores : 1;
@ -767,14 +768,30 @@ static void smp_parse(MachineState *ms, SMPConfiguration *config, Error **errp)
} else {
maxcpus = maxcpus > 0 ? maxcpus : cpus;
if (sockets == 0) {
cores = cores > 0 ? cores : 1;
threads = threads > 0 ? threads : 1;
sockets = maxcpus / (cores * threads);
} else if (cores == 0) {
threads = threads > 0 ? threads : 1;
cores = maxcpus / (sockets * threads);
} else if (threads == 0) {
if (mc->smp_prefer_sockets) {
/* prefer sockets over cores before 6.2 */
if (sockets == 0) {
cores = cores > 0 ? cores : 1;
threads = threads > 0 ? threads : 1;
sockets = maxcpus / (cores * threads);
} else if (cores == 0) {
threads = threads > 0 ? threads : 1;
cores = maxcpus / (sockets * 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 * threads);
} else if (sockets == 0) {
threads = threads > 0 ? threads : 1;
sockets = maxcpus / (cores * threads);
}
}
/* try to calculate omitted threads at last */
if (threads == 0) {
threads = maxcpus / (sockets * cores);
}
}

35
hw/i386/pc.c
View file

@ -716,6 +716,7 @@ void pc_acpi_smi_interrupt(void *opaque, int irq, int level)
*/
static void pc_smp_parse(MachineState *ms, 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;
@ -726,7 +727,7 @@ static void pc_smp_parse(MachineState *ms, SMPConfiguration *config, Error **err
/* directly default dies to 1 if it's omitted */
dies = dies > 0 ? dies : 1;
/* compute missing values, prefer sockets over cores over threads */
/* compute missing values based on the provided ones */
if (cpus == 0 && maxcpus == 0) {
sockets = sockets > 0 ? sockets : 1;
cores = cores > 0 ? cores : 1;
@ -734,14 +735,30 @@ static void pc_smp_parse(MachineState *ms, SMPConfiguration *config, Error **err
} else {
maxcpus = maxcpus > 0 ? maxcpus : cpus;
if (sockets == 0) {
cores = cores > 0 ? cores : 1;
threads = threads > 0 ? threads : 1;
sockets = maxcpus / (dies * cores * threads);
} else if (cores == 0) {
threads = threads > 0 ? threads : 1;
cores = maxcpus / (sockets * dies * threads);
} else if (threads == 0) {
if (mc->smp_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 * cores * threads);
} else if (cores == 0) {
threads = threads > 0 ? threads : 1;
cores = maxcpus / (sockets * dies * 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);
} else if (sockets == 0) {
threads = threads > 0 ? threads : 1;
sockets = maxcpus / (dies * cores * threads);
}
}
/* try to calculate omitted threads at last */
if (threads == 0) {
threads = maxcpus / (sockets * dies * cores);
}
}

1
hw/i386/pc_piix.c
View file

@ -432,6 +432,7 @@ static void pc_i440fx_6_1_machine_options(MachineClass *m)
m->is_default = false;
compat_props_add(m->compat_props, hw_compat_6_1, hw_compat_6_1_len);
compat_props_add(m->compat_props, pc_compat_6_1, pc_compat_6_1_len);
m->smp_prefer_sockets = true;
}
DEFINE_I440FX_MACHINE(v6_1, "pc-i440fx-6.1", NULL,

1
hw/i386/pc_q35.c
View file

@ -372,6 +372,7 @@ static void pc_q35_6_1_machine_options(MachineClass *m)
m->alias = NULL;
compat_props_add(m->compat_props, hw_compat_6_1, hw_compat_6_1_len);
compat_props_add(m->compat_props, pc_compat_6_1, pc_compat_6_1_len);
m->smp_prefer_sockets = true;
}
DEFINE_Q35_MACHINE(v6_1, "pc-q35-6.1", NULL,

1
hw/ppc/spapr.c
View file

@ -4685,6 +4685,7 @@ static void spapr_machine_6_1_class_options(MachineClass *mc)
spapr_machine_6_2_class_options(mc);
compat_props_add(mc->compat_props, hw_compat_6_1, hw_compat_6_1_len);
smc->pre_6_2_numa_affinity = true;
mc->smp_prefer_sockets = true;
}
DEFINE_SPAPR_MACHINE(6_1, "6.1", false);

1
hw/s390x/s390-virtio-ccw.c
View file

@ -814,6 +814,7 @@ static void ccw_machine_6_1_class_options(MachineClass *mc)
{
ccw_machine_6_2_class_options(mc);
compat_props_add(mc->compat_props, hw_compat_6_1, hw_compat_6_1_len);
mc->smp_prefer_sockets = true;
}
DEFINE_CCW_MACHINE(6_1, "6.1", false);

1
include/hw/boards.h
View file

@ -247,6 +247,7 @@ struct MachineClass {
bool nvdimm_supported;
bool numa_mem_supported;
bool auto_enable_numa;
bool smp_prefer_sockets;
const char *default_ram_id;
HotplugHandler *(*get_hotplug_handler)(MachineState *machine,

3
qemu-options.hx
View file

@ -244,7 +244,8 @@ SRST
Historically preference was given to the coarsest topology parameters
when computing missing values (ie sockets preferred over cores, which
were preferred over threads), however, this behaviour is considered
liable to change.
liable to change. Prior to 6.2 the preference was sockets over cores
over threads. Since 6.2 the preference is cores over sockets over threads.
ERST
DEF("numa", HAS_ARG, QEMU_OPTION_numa,