linux-kernel - [patch 23/30] x86/cpu/topology: Simplify cpu_mark_primary

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Date: Tue, 13 Feb 2024 22:06:06 +0100 (CET)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: x86@...nel.org,
 Tom Lendacky <thomas.lendacky@....com>,
 Andrew Cooper <andrew.cooper3@...rix.com>,
 Arjan van de Ven <arjan@...ux.intel.com>,
 Huang Rui <ray.huang@....com>,
 Juergen Gross <jgross@...e.com>,
 Dimitri Sivanich <dimitri.sivanich@....com>,
 Sohil Mehta <sohil.mehta@...el.com>,
 K Prateek Nayak <kprateek.nayak@....com>,
 Kan Liang <kan.liang@...ux.intel.com>,
 Zhang Rui <rui.zhang@...el.com>,
 "Paul E. McKenney" <paulmck@...nel.org>,
 Feng Tang <feng.tang@...el.com>,
 Andy Shevchenko <andy@...radead.org>,
 Michael Kelley <mhklinux@...look.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [patch 23/30] x86/cpu/topology: Simplify cpu_mark_primary_thread()

From: Thomas Gleixner <tglx@...utronix.de>

No point in creating a mask via fls(). smp_num_siblings is guaranteed to be
a power of 2. So just using (smp_num_siblings - 1) has the same effect.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

---
 arch/x86/kernel/cpu/topology.c |    5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)
---

--- a/arch/x86/kernel/cpu/topology.c
+++ b/arch/x86/kernel/cpu/topology.c
@@ -76,10 +76,7 @@ bool arch_match_cpu_phys_id(int cpu, u64
 #ifdef CONFIG_SMP
 static void cpu_mark_primary_thread(unsigned int cpu, unsigned int apicid)
 {
-	/* Isolate the SMT bit(s) in the APICID and check for 0 */
-	u32 mask = (1U << (fls(smp_num_siblings) - 1)) - 1;
-
-	if (smp_num_siblings == 1 || !(apicid & mask))
+	if (!(apicid & (smp_num_siblings - 1)))
 		cpumask_set_cpu(cpu, &__cpu_primary_thread_mask);
 }
 #else