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Expose threads-per-core and physical core count information

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With new sysctls (to the best of our ability do detect them).  Restructured
smp.4 slightly for clarity (keep relevant stuff closer to the top) while
documenting.

Reviewed by:	markj, jhibbits (ppc parts)
MFC after:	3 days
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D18322
This commit is contained in:
Conrad Meyer 2019-01-04 18:31:17 +00:00
parent 98ae4866ba
commit 6b83069e05
8 changed files with 90 additions and 29 deletions
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80
share/man/man4/smp.4
View File

@ -23,7 +23,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd January 6, 2018
.Dd January 4, 2019
.Dt SMP 4
.Os
.Sh NAME
@ -35,27 +35,6 @@
The
.Nm
kernel implements symmetric multi-processor support.
.Sh COMPATIBILITY
Support for multi-processor systems is present for all Tier-1
architectures on
.Fx .
Currently, this includes amd64, i386 and sparc64.
Support is enabled using
.Cd options SMP .
It is permissible to use the SMP kernel configuration on non-SMP equipped
motherboards.
.Sh I386 NOTES
For i386 systems, the
.Nm
kernel supports motherboards that follow the Intel MP specification,
version 1.4.
In addition to
.Cd options SMP ,
i386 also requires
.Cd device apic .
The
.Xr mptable 1
command may be used to view the status of multi-processor support.
.Pp
.Nm
support can be disabled by setting the loader tunable
@ -66,6 +45,13 @@ The number of CPUs detected by the system is available in
the read-only sysctl variable
.Va hw.ncpu .
.Pp
The number of online threads per CPU core is available in the read-only sysctl
variable
.Va kern.smp.threads_per_core .
The number of physical CPU cores detected by the system is available in the
read-only sysctl variable
.Va kern.smp.cores .
.Pp
.Fx
allows specific CPUs on a multi-processor system to be disabled.
This can be done using the
@ -74,6 +60,12 @@ tunable, where X is the APIC ID of a CPU.
Setting this tunable to 1 will result in the corresponding CPU being
disabled.
.Pp
.Fx
supports simultaneous multithreading on x86 and powerpc platforms.
On x86, the logical CPUs can be disabled by setting the
.Va machdep.hyperthreading_allowed
tunable to zero.
.Pp
The
.Xr sched_ule 4
scheduler implements CPU topology detection and adjusts the scheduling
@ -122,13 +114,26 @@ two quad-core processors is:
.Pp
This information is used internally by the kernel to schedule related
tasks on CPUs that are closely grouped together.
.Pp
.Fx
supports hyperthreading on Intel CPU's on the i386 and AMD64 platforms.
Because using logical CPUs can cause performance penalties under certain loads,
the logical CPUs can be disabled by setting the
.Va machdep.hyperthreading_allowed
tunable to zero.
.Sh COMPATIBILITY
Support for multi-processor systems is present for all Tier-1 and Tier-2
architectures on
.Fx .
Currently, this includes x86, powerpc, arm, and sparc64.
Support is enabled using
.Cd options SMP .
It is permissible to use the SMP kernel configuration on non-SMP hardware.
.Sh I386 NOTES
For i386 systems, the
.Nm
kernel supports motherboards that follow the Intel MP specification,
version 1.4.
In addition to
.Cd options SMP ,
i386 also requires
.Cd device apic .
The
.Xr mptable 1
command may be used to view the status of multi-processor support.
.Sh SEE ALSO
.Xr cpuset 1 ,
.Xr mptable 1 ,
@ -166,3 +171,20 @@ in
also introduced support for SMP on the sparc64 architecture.
.Sh AUTHORS
.An Steve Passe Aq Mt fsmp@FreeBSD.org
.Sh CAVEATS
The
.Va kern.smp.threads_per_core
and
.Va kern.smp.cores
sysctl variables are provided as a best-effort guess.
If an architecture or platform adds SMT and
.Fx
has not yet implemented detection, the reported values may be inaccurate.
In this case,
.Va kern.smp.threads_per_core
will report
.Dv 1
and
.Va kern.smp.cores
will report the same value as
.Va hw.ncpu .

15
sys/kern/subr_smp.c
View File

@ -98,6 +98,14 @@ int smp_cpus = 1; /* how many cpu's running */
SYSCTL_INT(_kern_smp, OID_AUTO, cpus, CTLFLAG_RD|CTLFLAG_CAPRD, &smp_cpus, 0,
"Number of CPUs online");
int smp_threads_per_core = 1; /* how many SMT threads are running per core */
SYSCTL_INT(_kern_smp, OID_AUTO, threads_per_core, CTLFLAG_RD|CTLFLAG_CAPRD,
&smp_threads_per_core, 0, "Number of SMT threads online per core");
int mp_ncores = -1; /* how many physical cores running */
SYSCTL_INT(_kern_smp, OID_AUTO, cores, CTLFLAG_RD|CTLFLAG_CAPRD, &mp_ncores, 0,
"Number of CPUs online");
int smp_topology = 0; /* Which topology we're using. */
SYSCTL_INT(_kern_smp, OID_AUTO, topology, CTLFLAG_RDTUN, &smp_topology, 0,
"Topology override setting; 0 is default provided by hardware.");
@ -154,6 +162,7 @@ mp_start(void *dummy)
/* Probe for MP hardware. */
if (smp_disabled != 0 || cpu_mp_probe() == 0) {
mp_ncores = 1;
mp_ncpus = 1;
CPU_SETOF(PCPU_GET(cpuid), &all_cpus);
return;
@ -162,6 +171,11 @@ mp_start(void *dummy)
cpu_mp_start();
printf("FreeBSD/SMP: Multiprocessor System Detected: %d CPUs\n",
mp_ncpus);
/* Provide a default for most architectures that don't have SMT/HTT. */
if (mp_ncores < 0)
mp_ncores = mp_ncpus;
cpu_mp_announce();
}
SYSINIT(cpu_mp, SI_SUB_CPU, SI_ORDER_THIRD, mp_start, NULL);
@ -823,6 +837,7 @@ static void
mp_setvariables_for_up(void *dummy)
{
mp_ncpus = 1;
mp_ncores = 1;
mp_maxid = PCPU_GET(cpuid);
CPU_SETOF(mp_maxid, &all_cpus);
KASSERT(PCPU_GET(cpuid) == 0, ("UP must have a CPU ID of zero"));

4
sys/powerpc/powernv/platform_powernv.c
View File

@ -435,6 +435,8 @@ powernv_smp_topo(platform_t plat)
break;
}
smp_threads_per_core = nthreads;
if (mp_ncpus % nthreads != 0) {
printf("WARNING: Irregular SMP topology. Performance may be "
"suboptimal (%d threads, %d on first core)\n",
@ -442,6 +444,8 @@ powernv_smp_topo(platform_t plat)
return (smp_topo_none());
}
mp_ncores = mp_ncpus / nthreads;
/* Don't do anything fancier for non-threaded SMP */
if (nthreads == 1)
return (smp_topo_none());

5
sys/powerpc/powerpc/mp_machdep.c
View File

@ -186,6 +186,11 @@ cpu_mp_start(void)
next:
error = platform_smp_next_cpu(&cpu);
}
#ifdef SMP
/* Probe mp_ncores and smp_threads_per_core as a side effect. */
(void)cpu_topo();
#endif
}
void

2
sys/powerpc/ps3/platform_ps3.c
View File

@ -246,6 +246,8 @@ ps3_smp_start_cpu(platform_t plat, struct pcpu *pc)
static struct cpu_group *
ps3_smp_topo(platform_t plat)
{
mp_ncores = 1;
smp_threads_per_core = 2;
return (smp_topo_1level(CG_SHARE_L1, 2, CG_FLAG_SMT));
}
#endif

3
sys/powerpc/pseries/platform_chrp.c
View File

@ -517,6 +517,8 @@ chrp_smp_topo(platform_t plat)
ncpus++;
}
mp_ncores = ncores;
if (ncpus % ncores != 0) {
printf("WARNING: Irregular SMP topology. Performance may be "
"suboptimal (%d CPUS, %d cores)\n", ncpus, ncores);
@ -527,6 +529,7 @@ chrp_smp_topo(platform_t plat)
if (ncpus == ncores)
return (smp_topo_none());
smp_threads_per_core = ncpus / ncores;
return (smp_topo_1level(CG_SHARE_L1, ncpus / ncores, CG_FLAG_SMT));
}
#endif

2
sys/sys/smp.h
View File

@ -167,8 +167,10 @@ extern cpuset_t logical_cpus_mask;
extern u_int mp_maxid;
extern int mp_maxcpus;
extern int mp_ncores;
extern int mp_ncpus;
extern volatile int smp_started;
extern int smp_threads_per_core;
extern cpuset_t all_cpus;
extern cpuset_t cpuset_domain[MAXMEMDOM]; /* CPUs in each NUMA domain. */

8
sys/x86/x86/mp_x86.c
View File

@ -607,6 +607,7 @@ assign_cpu_ids(void)
{
struct topo_node *node;
u_int smt_mask;
int nhyper;
smt_mask = (1u << core_id_shift) - 1;
@ -615,6 +616,7 @@ assign_cpu_ids(void)
* beyond MAXCPU. CPU 0 is always assigned to the BSP.
*/
mp_ncpus = 0;
nhyper = 0;
TOPO_FOREACH(node, &topo_root) {
if (node->type != TOPO_TYPE_PU)
continue;
@ -642,6 +644,9 @@ assign_cpu_ids(void)
continue;
}
if (cpu_info[node->hwid].cpu_hyperthread)
nhyper++;
cpu_apic_ids[mp_ncpus] = node->hwid;
apic_cpuids[node->hwid] = mp_ncpus;
topo_set_pu_id(node, mp_ncpus);
@ -651,6 +656,9 @@ assign_cpu_ids(void)
KASSERT(mp_maxid >= mp_ncpus - 1,
("%s: counters out of sync: max %d, count %d", __func__, mp_maxid,
mp_ncpus));
mp_ncores = mp_ncpus - nhyper;
smp_threads_per_core = mp_ncpus / mp_ncores;
}
/*