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

[Atish Patra]

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.pa...@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