linux-kernel - [v2 PATCH] RISC-V: Optimize tlb flush path.

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Message-Id: <20190820004735.18518-1-atish.patra@wdc.com>
Date:   Mon, 19 Aug 2019 17:47:35 -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>,
        Allison Randal <allison@...utok.net>,
        Anup Patel <anup@...infault.org>,
        linux-riscv@...ts.infradead.org,
        Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Andreas Schwab <schwab@...ux-m68k.org>,
        "hch@...radead.org" <hch@...radead.org>
Subject: [v2 PATCH] RISC-V: Optimize tlb flush path.

In RISC-V, tlb flush happens via SBI which is expensive.
If the target cpumask contains a local hartid, some cost
can be saved by issuing a local tlb flush as we do that
in OpenSBI anyways. There is also no need of SBI call if
cpumask is empty.

Do a local flush first if current cpu is present in cpumask.
Invoke SBI call only if target cpumask contains any cpus
other than local cpu.

Signed-off-by: Atish Patra <atish.patra@....com>
---
 arch/riscv/include/asm/tlbflush.h | 37 ++++++++++++++++++++++++++-----
 1 file changed, 31 insertions(+), 6 deletions(-)

diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index b5e64dc19b9e..3f9cd17b5402 100644
--- a/arch/riscv/include/asm/tlbflush.h
+++ b/arch/riscv/include/asm/tlbflush.h
@@ -8,6 +8,7 @@
 #define _ASM_RISCV_TLBFLUSH_H
 
 #include <linux/mm_types.h>
+#include <linux/sched.h>
 #include <asm/smp.h>
 
 /*
@@ -42,20 +43,44 @@ static inline void flush_tlb_range(struct vm_area_struct *vma,
 
 #include <asm/sbi.h>
 
-static inline void remote_sfence_vma(struct cpumask *cmask, unsigned long start,
-				     unsigned long size)
+static void __riscv_flush_tlb(struct cpumask *cmask, unsigned long start,
+			      unsigned long size)
 {
 	struct cpumask hmask;
+	unsigned int hartid;
+	unsigned int cpuid;
 
 	cpumask_clear(&hmask);
+
+	if (!cmask) {
+		riscv_cpuid_to_hartid_mask(cpu_online_mask, &hmask);
+		goto issue_sfence;
+	}
+
+	cpuid = get_cpu();
+	if (cpumask_test_cpu(cpuid, cmask)) {
+		/* Save trap cost by issuing a local tlb flush here */
+		if ((start == 0 && size == -1) || (size > PAGE_SIZE))
+			local_flush_tlb_all();
+		else if (size == PAGE_SIZE)
+			local_flush_tlb_page(start);
+	}
+	if (cpumask_any_but(cmask, cpuid) >= nr_cpu_ids)
+		goto done;
+
 	riscv_cpuid_to_hartid_mask(cmask, &hmask);
+	hartid = cpuid_to_hartid_map(cpuid);
+	cpumask_clear_cpu(hartid, &hmask);
+
+issue_sfence:
 	sbi_remote_sfence_vma(hmask.bits, start, size);
+done:
+	put_cpu();
 }
 
-#define flush_tlb_all() sbi_remote_sfence_vma(NULL, 0, -1)
-
+#define flush_tlb_all() __riscv_flush_tlb(NULL, 0, -1)
 #define flush_tlb_range(vma, start, end) \
-	remote_sfence_vma(mm_cpumask((vma)->vm_mm), start, (end) - (start))
+	__riscv_flush_tlb(mm_cpumask((vma)->vm_mm), start, (end) - (start))
 
 static inline void flush_tlb_page(struct vm_area_struct *vma,
 				  unsigned long addr) {
@@ -63,7 +88,7 @@ static inline void flush_tlb_page(struct vm_area_struct *vma,
 }
 
 #define flush_tlb_mm(mm)				\
-	remote_sfence_vma(mm_cpumask(mm), 0, -1)
+	__riscv_flush_tlb(mm_cpumask(mm), 0, -1)
 
 #endif /* CONFIG_SMP */
 
-- 
2.21.0