linux-kernel - [PATCH] x86/smpboot: Decrapify build_sched

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Message-ID: <87frfuqusq.ffs@tglx>
Date: Fri, 20 Jun 2025 17:47:33 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Li Chen <me@...ux.beauty>
Cc: Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>, Dave
 Hansen <dave.hansen@...ux.intel.com>, x86 <x86@...nel.org>, linux-kernel
 <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/smpboot: Decrapify build_sched_topology()

The #ifdeffery and the initializers in build_sched_topology() are just
disgusting. The SCHED_SMT #ifdef is also pointless because SCHED_SMT is
unconditionally enabled when SMP is enabled.

Statically initialize the domain levels in the topology array and let
build_sched_topology() invalidate the package domain level when NUMA in
package is available.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
Note: This allows to remove the SMT level with a simple memmove()
---
 arch/x86/kernel/smpboot.c |   45 +++++++++++++++++----------------------------
 1 file changed, 17 insertions(+), 28 deletions(-)

--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -478,43 +478,32 @@ static int x86_cluster_flags(void)
  */
 static bool x86_has_numa_in_package;
 
-static struct sched_domain_topology_level x86_topology[6];
+#define DOMAIN(maskfn, flagsfn, dname) { .mask = maskfn, .sd_flags = flagsfn, .name = #dname }
 
-static void __init build_sched_topology(void)
-{
-	int i = 0;
-
-#ifdef CONFIG_SCHED_SMT
-	x86_topology[i++] = (struct sched_domain_topology_level){
-		cpu_smt_mask, cpu_smt_flags, SD_INIT_NAME(SMT)
-	};
-#endif
+static struct sched_domain_topology_level x86_topology[] = {
+	DOMAIN(cpu_smt_mask, cpu_smt_flags, SMT),
 #ifdef CONFIG_SCHED_CLUSTER
-	x86_topology[i++] = (struct sched_domain_topology_level){
-		cpu_clustergroup_mask, x86_cluster_flags, SD_INIT_NAME(CLS)
-	};
+	DOMAIN(cpu_clustergroup_mask, x86_cluster_flags, CLS),
 #endif
 #ifdef CONFIG_SCHED_MC
-	x86_topology[i++] = (struct sched_domain_topology_level){
-		cpu_coregroup_mask, x86_core_flags, SD_INIT_NAME(MC)
-	};
+	DOMAIN(cpu_coregroup_mask, x86_core_flags, MC),
 #endif
-	/*
-	 * When there is NUMA topology inside the package skip the PKG domain
-	 * since the NUMA domains will auto-magically create the right spanning
-	 * domains based on the SLIT.
-	 */
-	if (!x86_has_numa_in_package) {
-		x86_topology[i++] = (struct sched_domain_topology_level){
-			cpu_cpu_mask, x86_sched_itmt_flags, SD_INIT_NAME(PKG)
-		};
-	}
+	DOMAIN(cpu_cpu_mask, x86_sched_itmt_flags, PKG),
+	{ NULL },
+};
 
+static void __init build_sched_topology(void)
+{
 	/*
-	 * There must be one trailing NULL entry left.
+	 * When there is NUMA topology inside the package invalidate the
+	 * PKG domain since the NUMA domains will auto-magically create the
+	 * right spanning domains based on the SLIT.
 	 */
-	BUG_ON(i >= ARRAY_SIZE(x86_topology)-1);
+	if (x86_has_numa_in_package) {
+		unsigned int pkgdom = ARRAY_SIZE(x86_topology) - 2;
 
+		memset(&x86_topology[pkgdom], 0, sizeof(x86_topology[pkgdom]));
+	}
 	set_sched_topology(x86_topology);
 }