From: Rik van Riel Date: Sat, 9 Nov 2024 00:27:50 +0000 (-0500) Subject: x86/mm/tlb: Put cpumask_test_cpu() check in switch_mm_irqs_off() under CONFIG_DEBUG_VM X-Git-Tag: v6.13-rc1~175^2 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=7e33001b8b9a78062679e0fdf5b0842a49063135;p=linux-2.6-block.git x86/mm/tlb: Put cpumask_test_cpu() check in switch_mm_irqs_off() under CONFIG_DEBUG_VM On a web server workload, the cpumask_test_cpu() inside the WARN_ON_ONCE() in the 'prev == next branch' takes about 17% of all the CPU time of switch_mm_irqs_off(). On a large fleet, this WARN_ON_ONCE() has not fired in at least a month, possibly never. Move this test under CONFIG_DEBUG_VM so it does not get compiled in production kernels. Signed-off-by: Rik van Riel Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: Peter Zijlstra Cc: Linus Torvalds Link: https://lore.kernel.org/r/20241109003727.3958374-4-riel@surriel.com --- diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 86593d1b787d..b0d5a644fc84 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -568,7 +568,7 @@ void switch_mm_irqs_off(struct mm_struct *unused, struct mm_struct *next, * mm_cpumask. The TLB shootdown code can figure out from * cpu_tlbstate_shared.is_lazy whether or not to send an IPI. */ - if (WARN_ON_ONCE(prev != &init_mm && + if (IS_ENABLED(CONFIG_DEBUG_VM) && WARN_ON_ONCE(prev != &init_mm && !cpumask_test_cpu(cpu, mm_cpumask(next)))) cpumask_set_cpu(cpu, mm_cpumask(next));