The following commit has been merged into the x86/mm branch of tip: Commit-ID: 7e33001b8b9a78062679e0fdf5b0842a49063135 Gitweb: https://git.kernel.org/tip/7e33001b8b9a78062679e0fdf5b0842a49063135 Author: Rik van Riel <riel@xxxxxxxxxxx> AuthorDate: Fri, 08 Nov 2024 19:27:50 -05:00 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Wed, 13 Nov 2024 03:42:41 +01:00 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 <riel@xxxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20241109003727.3958374-4-riel@xxxxxxxxxxx --- arch/x86/mm/tlb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 86593d1..b0d5a64 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));
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