Re: [PATCH v2 1/7] powerpc/64s/radix: do not flush TLB on spurious fault
From: Aneesh Kumar K.V <hidden>
Date: 2018-05-21 06:06:25
Nicholas Piggin [off-list ref] writes:
In the case of a spurious fault (which can happen due to a race with
another thread that changes the page table), the default Linux mm code
calls flush_tlb_page for that address. This is not required because
the pte will be re-fetched. Hash does not wire this up to a hardware
TLB flush for this reason. This patch avoids the flush for radix.
From Power ISA v3.0B, p.1090:
Setting a Reference or Change Bit or Upgrading Access Authority
(PTE Subject to Atomic Hardware Updates)
If the only change being made to a valid PTE that is subject to
atomic hardware updates is to set the Refer- ence or Change bit to
1 or to add access authorities, a simpler sequence suffices
because the translation hardware will refetch the PTE if an access
is attempted for which the only problems were reference and/or
change bits needing to be set or insufficient access authority.
The nest MMU on POWER9 does not re-fetch the PTE after such an access
attempt before faulting, so address spaces with a coprocessor
attached will continue to flush in these cases.
This reduces tlbies for a kernel compile workload from 0.95M to 0.90M.
fork --fork --exec benchmark improved 0.5% (12300->12400).Reviewed-by: Aneesh Kumar K.V <redacted> Do you want to use flush_tlb_fix_spurious_fault in ptep_set_access_flags() also?. That would bring it closer to generic version?
quoted hunk ↗ jump to hunk
Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- Since v1: - Added NMMU handling arch/powerpc/include/asm/book3s/64/tlbflush.h | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush.h b/arch/powerpc/include/asm/book3s/64/tlbflush.h index 0cac17253513..ebf572ea621e 100644 --- a/arch/powerpc/include/asm/book3s/64/tlbflush.h +++ b/arch/powerpc/include/asm/book3s/64/tlbflush.h@@ -4,7 +4,7 @@ #define MMU_NO_CONTEXT ~0UL - +#include <linux/mm_types.h> #include <asm/book3s/64/tlbflush-hash.h> #include <asm/book3s/64/tlbflush-radix.h>@@ -137,6 +137,16 @@ static inline void flush_all_mm(struct mm_struct *mm) #define flush_tlb_page(vma, addr) local_flush_tlb_page(vma, addr) #define flush_all_mm(mm) local_flush_all_mm(mm) #endif /* CONFIG_SMP */ + +#define flush_tlb_fix_spurious_fault flush_tlb_fix_spurious_fault +static inline void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma, + unsigned long address) +{ + /* See ptep_set_access_flags comment */ + if (atomic_read(&vma->vm_mm->context.copros) > 0) + flush_tlb_page(vma, address); +} + /* * flush the page walk cache for the address */-- 2.17.0