From c4885bbb3afee80f41d39a33e49881a18e500f47 Mon Sep 17 00:00:00 2001 From: Pingfan Liu Date: Fri, 10 Jul 2020 22:04:12 +0800 Subject: arm64/mm: save memory access in check_and_switch_context() fast switch path On arm64, smp_processor_id() reads a per-cpu `cpu_number` variable, using the per-cpu offset stored in the tpidr_el1 system register. In some cases we generate a per-cpu address with a sequence like: cpu_ptr = &per_cpu(ptr, smp_processor_id()); Which potentially incurs a cache miss for both `cpu_number` and the in-memory `__per_cpu_offset` array. This can be written more optimally as: cpu_ptr = this_cpu_ptr(ptr); Which only needs the offset from tpidr_el1, and does not need to load from memory. The following two test cases show a small performance improvement measured on a 46-cpus qualcomm machine with 5.8.0-rc4 kernel. Test 1: (about 0.3% improvement) #cat b.sh make clean && make all -j138 #perf stat --repeat 10 --null --sync sh b.sh - before this patch Performance counter stats for 'sh b.sh' (10 runs): 298.62 +- 1.86 seconds time elapsed ( +- 0.62% ) - after this patch Performance counter stats for 'sh b.sh' (10 runs): 297.734 +- 0.954 seconds time elapsed ( +- 0.32% ) Test 2: (about 1.69% improvement) 'perf stat -r 10 perf bench sched messaging' Then sum the total time of 'sched/messaging' by manual. - before this patch total 0.707 sec for 10 times - after this patch totol 0.695 sec for 10 times Signed-off-by: Pingfan Liu Acked-by: Mark Rutland Cc: Will Deacon Cc: Steve Capper Cc: Mark Rutland Cc: Vladimir Murzin Cc: Jean-Philippe Brucker Link: https://lore.kernel.org/r/1594389852-19949-1-git-send-email-kernelfans@gmail.com Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/mmu_context.h | 6 ++---- arch/arm64/mm/context.c | 10 ++++++---- 2 files changed, 8 insertions(+), 8 deletions(-) (limited to 'arch') diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h index b0bd9b55594c..f2d7537d6f83 100644 --- a/arch/arm64/include/asm/mmu_context.h +++ b/arch/arm64/include/asm/mmu_context.h @@ -175,7 +175,7 @@ static inline void cpu_replace_ttbr1(pgd_t *pgdp) * take CPU migration into account. */ #define destroy_context(mm) do { } while(0) -void check_and_switch_context(struct mm_struct *mm, unsigned int cpu); +void check_and_switch_context(struct mm_struct *mm); #define init_new_context(tsk,mm) ({ atomic64_set(&(mm)->context.id, 0); 0; }) @@ -214,8 +214,6 @@ enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk) static inline void __switch_mm(struct mm_struct *next) { - unsigned int cpu = smp_processor_id(); - /* * init_mm.pgd does not contain any user mappings and it is always * active for kernel addresses in TTBR1. Just set the reserved TTBR0. @@ -225,7 +223,7 @@ static inline void __switch_mm(struct mm_struct *next) return; } - check_and_switch_context(next, cpu); + check_and_switch_context(next); } static inline void diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c index d702d60e64da..a206655a39a5 100644 --- a/arch/arm64/mm/context.c +++ b/arch/arm64/mm/context.c @@ -198,9 +198,10 @@ set_asid: return idx2asid(asid) | generation; } -void check_and_switch_context(struct mm_struct *mm, unsigned int cpu) +void check_and_switch_context(struct mm_struct *mm) { unsigned long flags; + unsigned int cpu; u64 asid, old_active_asid; if (system_supports_cnp()) @@ -222,9 +223,9 @@ void check_and_switch_context(struct mm_struct *mm, unsigned int cpu) * relaxed xchg in flush_context will treat us as reserved * because atomic RmWs are totally ordered for a given location. */ - old_active_asid = atomic64_read(&per_cpu(active_asids, cpu)); + old_active_asid = atomic64_read(this_cpu_ptr(&active_asids)); if (old_active_asid && asid_gen_match(asid) && - atomic64_cmpxchg_relaxed(&per_cpu(active_asids, cpu), + atomic64_cmpxchg_relaxed(this_cpu_ptr(&active_asids), old_active_asid, asid)) goto switch_mm_fastpath; @@ -236,10 +237,11 @@ void check_and_switch_context(struct mm_struct *mm, unsigned int cpu) atomic64_set(&mm->context.id, asid); } + cpu = smp_processor_id(); if (cpumask_test_and_clear_cpu(cpu, &tlb_flush_pending)) local_flush_tlb_all(); - atomic64_set(&per_cpu(active_asids, cpu), asid); + atomic64_set(this_cpu_ptr(&active_asids), asid); raw_spin_unlock_irqrestore(&cpu_asid_lock, flags); switch_mm_fastpath: -- cgit v1.2.3