From: Li Chen Date: Thu, 10 Jul 2025 10:57:10 +0000 (+0800) Subject: x86/smpboot: avoid SMT domain attach/destroy if SMT is not enabled X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f79c9aa446d638190578515afcd06d6c9d72da55;p=thirdparty%2Fkernel%2Fstable.git x86/smpboot: avoid SMT domain attach/destroy if SMT is not enabled 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 Signed-off-by: Li Chen Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: K Prateek Nayak Tested-by: K Prateek Nayak Link: https://lore.kernel.org/r/20250710105715.66594-5-me@linux.beauty --- diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 8038286454cf..412c813cd268 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -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)