linux-kernel - [PATCH v3 1/3] RISC-V: Issue a local tlbflush if possible.

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Date:   Wed, 21 Aug 2019 17:46:42 -0700
From:   Atish Patra <atish.patra@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Atish Patra <atish.patra@....com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org,
        Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Christoph Hellwig <hch@....de>,
        Anup Patel <Anup.Patel@....com>,
        Andreas Schwab <schwab@...ux-m68k.org>
Subject: [PATCH v3 1/3] RISC-V: Issue a local tlbflush if possible.

In RISC-V, tlb flush happens via SBI which is expensive. If the local
cpu is the only cpu in cpumask, there is no need to invoke a SBI call.

Just do a local flush and return.

Signed-off-by: Atish Patra <atish.patra@....com>
---
 arch/riscv/mm/tlbflush.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index df93b26f1b9d..36430ee3bed9 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -2,6 +2,7 @@
 
 #include <linux/mm.h>
 #include <linux/smp.h>
+#include <linux/sched.h>
 #include <asm/sbi.h>
 
 void flush_tlb_all(void)
@@ -13,9 +14,23 @@ static void __sbi_tlb_flush_range(struct cpumask *cmask, unsigned long start,
 		unsigned long size)
 {
 	struct cpumask hmask;
+	unsigned int cpuid = get_cpu();
 
+	if (!cmask) {
+		riscv_cpuid_to_hartid_mask(cpu_online_mask, &hmask);
+		goto issue_sfence;
+	}
+
+	if (cpumask_test_cpu(cpuid, cmask) && cpumask_weight(cmask) == 1) {
+		local_flush_tlb_all();
+		goto done;
+	}
 	riscv_cpuid_to_hartid_mask(cmask, &hmask);
+
+issue_sfence:
 	sbi_remote_sfence_vma(hmask.bits, start, size);
+done:
+	put_cpu();
 }
 
 void flush_tlb_mm(struct mm_struct *mm)
-- 
2.21.0