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Subject[v2 PATCH] RISC-V: Optimize tlb flush path.
Date
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@wdc.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
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