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SubjectRe: [PATCH] RISC-V: Issue a local tlb flush if possible.
Date


On 8/9/19, 6:43 PM, "Atish Patra" <Atish.Patra@wdc.com> wrote:

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.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
---
arch/riscv/include/asm/tlbflush.h | 33 +++++++++++++++++++++++++++----
1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index 687dd19735a7..b32ba4fa5888 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>
/*
@@ -46,14 +47,38 @@ static inline void remote_sfence_vma(struct cpumask *cmask, unsigned long start,
unsigned long size)
{
struct cpumask hmask;
+ struct cpumask tmask;
+ int cpuid = smp_processor_id();

cpumask_clear(&hmask);
- riscv_cpuid_to_hartid_mask(cmask, &hmask);
- sbi_remote_sfence_vma(hmask.bits, start, size);
+ cpumask_clear(&tmask);
+
+ if (cmask)
+ cpumask_copy(&tmask, cmask);
+ else
+ cpumask_copy(&tmask, cpu_online_mask);
+
+ if (cpumask_test_cpu(cpuid, &tmask)) {
+ /* 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);
+ cpumask_clear_cpu(cpuid, &tmask);
+ } else if (cpumask_empty(&tmask)) {
+ /* cpumask is empty. So just do a local flush */
+ local_flush_tlb_all();
+ return;
+ }
+
+ if (!cpumask_empty(&tmask)) {
+ riscv_cpuid_to_hartid_mask(&tmask, &hmask);
+ sbi_remote_sfence_vma(hmask.bits, start, size);
+ }
}
-#define flush_tlb_all() sbi_remote_sfence_vma(NULL, 0, -1)
-#define flush_tlb_page(vma, addr) flush_tlb_range(vma, addr, 0)
+#define flush_tlb_all() remote_sfence_vma(NULL, 0, -1)
+#define flush_tlb_page(vma, addr) flush_tlb_range(vma, addr, (addr) + PAGE_SIZE)

I did not see Paul's patch to fix this. I will remove this in v2 and rebase on top of Paul's patch.

Regards,
Atish
#define flush_tlb_range(vma, start, end) \
remote_sfence_vma(mm_cpumask((vma)->vm_mm), start, (end) - (start))
#define flush_tlb_mm(mm) \
--
2.21.0



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