Messages in this thread | | | From | Atish Patra <> | Subject | Re: [v2 PATCH] RISC-V: Optimize tlb flush path. | Date | Tue, 20 Aug 2019 20:29:47 +0000 |
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On Tue, 2019-08-20 at 14:21 +0530, Anup Patel wrote: > On Tue, Aug 20, 2019 at 6:17 AM 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. 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 > > > > I think we should move __riscv_flush_tlb() to mm/tlbflush.c because > it's quite > big now. > > In future, we will also have __riscv_flush_tlb_asid() which will > flush TLB based > on ASID. >
Sounds good to me. Christoph has already mm/tlbflush.c in his mmu series. I will rebase on top of it.
> Regards, > Anup
-- Regards, Atish
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