linux-kernel - [PATCH] riscv: Optimize switch_mm by passing "cpu" to flush_icache

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Date:   Wed, 12 May 2021 01:42:31 +0800
From:   Jisheng Zhang <jszhang3@...l.ustc.edu.cn>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] riscv: Optimize switch_mm by passing "cpu" to
 flush_icache_deferred()

From: Jisheng Zhang <jszhang@...nel.org>

Directly passing the cpu to flush_icache_deferred() rather than calling
smp_processor_id() again.

Here are some performance numbers:

With a run of hackbench 30 times on a single core riscv64 Qemu instance
with 1GB memory:

without this patch: mean 36.934
with this patch: mean 36.104 (improved by 2.24%)

Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
---
 arch/riscv/mm/context.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
index 68aa312fc352..6d445f2888ec 100644
--- a/arch/riscv/mm/context.c
+++ b/arch/riscv/mm/context.c
@@ -281,10 +281,9 @@ static inline void set_mm(struct mm_struct *mm, unsigned int cpu)
  * actually performs that local instruction cache flush, which implicitly only
  * refers to the current hart.
  */
-static inline void flush_icache_deferred(struct mm_struct *mm)
+static inline void flush_icache_deferred(struct mm_struct *mm, unsigned int cpu)
 {
 #ifdef CONFIG_SMP
-	unsigned int cpu = smp_processor_id();
 	cpumask_t *mask = &mm->context.icache_stale_mask;
 
 	if (cpumask_test_cpu(cpu, mask)) {
@@ -320,5 +319,5 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 
 	set_mm(next, cpu);
 
-	flush_icache_deferred(next);
+	flush_icache_deferred(next, cpu);
 }
-- 
2.31.0