2019-08-22 08:53:03

by Atish Patra

Subject: [PATCH v4 2/3] 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 <[email protected]>
---
arch/riscv/mm/tlbflush.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 1293b8017ee0..8172fbf46123 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)
@@ -9,16 +10,30 @@ void flush_tlb_all(void)
sbi_remote_sfence_vma(NULL, 0, -1);
}

+/*
+ * This function must not be called with cmask being null.
+ * Kernel may panic if cmask is NULL.
+ */
static void __sbi_tlb_flush_range(struct cpumask *cmask, unsigned long start,
unsigned long size)
{
struct cpumask hmask;
+ unsigned int cpuid;

if (cpumask_empty(cmask))
return;

- riscv_cpuid_to_hartid_mask(cmask, &hmask);
- sbi_remote_sfence_vma(hmask.bits, start, size);
+ cpuid = get_cpu();
+
+ if (cpumask_any_but(cmask, cpuid) >= nr_cpu_ids) {
+ /* local cpu is the only cpu present in cpumask */
+ local_flush_tlb_all();
+ } else {
+ riscv_cpuid_to_hartid_mask(cmask, &hmask);
+ sbi_remote_sfence_vma(cpumask_bits(&hmask), start, size);
+ }
+
+ put_cpu();
}

void flush_tlb_mm(struct mm_struct *mm)
--
2.21.0

2019-08-22 10:27:36

by Christoph Hellwig

Subject: Re: [PATCH v4 2/3] RISC-V: Issue a local tlbflush if possible.

On Thu, Aug 22, 2019 at 12:51:50AM -0700, Atish Patra wrote:
> 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 <[email protected]>

Looks good,

Reviewed-by: Christoph Hellwig <[email protected]>