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x86/smpboot: avoid SMT domain attach/destroy if SMT is not enabled

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Currently, the SMT domain is added into sched_domain_topology by default.

If cpu_attach_domain() finds that the CPU SMT domain’s cpumask_weight
is just 1, it will destroy it.

On a large machine, such as one with 512 cores, this results in
512 redundant domain attach/destroy operations.

Avoid these unnecessary operations by simply checking
cpu_smt_num_threads and skip SMT domain if the SMT domain is not
enabled.

Suggested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lore.kernel.org/r/20250710105715.66594-5-me@linux.beauty
This commit is contained in:
Li Chen 2025-07-10 18:57:10 +08:00 committed by Peter Zijlstra
parent fbc2010d92
commit f79c9aa446
1 changed files with 11 additions and 1 deletions
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12
arch/x86/kernel/smpboot.c
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@ -492,6 +492,8 @@ static struct sched_domain_topology_level x86_topology[] = {
static void __init build_sched_topology(void)
{
struct sched_domain_topology_level *topology = x86_topology;
/*
* When there is NUMA topology inside the package invalidate the
* PKG domain since the NUMA domains will auto-magically create the
@ -502,7 +504,15 @@ static void __init build_sched_topology(void)
memset(&x86_topology[pkgdom], 0, sizeof(x86_topology[pkgdom]));
}
set_sched_topology(x86_topology);
/*
* Drop the SMT domains if there is only one thread per-core
* since it'll get degenerated by the scheduler anyways.
*/
if (cpu_smt_num_threads <= 1)
++topology;
set_sched_topology(topology);
}
void set_cpu_sibling_map(int cpu)