On Fri, 6 Apr 2018 03:56:31 +1000
Nicholas Piggin <npiggin@xxxxxxxxx> wrote:
> tlbies to an LPAR do not have to be serialised since POWER4,
> MMU_FTR_LOCKLESS_TLBIE can be used to avoid the spin lock in
> do_tlbies.
>
> Testing was done on a POWER9 system in HPT mode, with a -smp 32 guest
> in HPT mode. 32 instances of the powerpc fork benchmark from selftests
> were run with --fork, and the results measured.
>
> Without this patch, total throughput was about 13.5K/sec, and this is
> the top of the host profile:
>
> 74.52% [k] do_tlbies
> 2.95% [k] kvmppc_book3s_hv_page_fault
> 1.80% [k] calc_checksum
> 1.80% [k] kvmppc_vcpu_run_hv
> 1.49% [k] kvmppc_run_core
>
> After this patch, throughput was about 51K/sec, with this profile:
>
> 21.28% [k] do_tlbies
> 5.26% [k] kvmppc_run_core
> 4.88% [k] kvmppc_book3s_hv_page_fault
> 3.30% [k] _raw_spin_lock_irqsave
> 3.25% [k] gup_pgd_range
>
> Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
> ---
> arch/powerpc/kvm/book3s_hv_rm_mmu.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> index 78e6a392330f..0221a0f74f07 100644
> --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> @@ -439,6 +439,9 @@ static inline int try_lock_tlbie(unsigned int *lock)
> unsigned int tmp, old;
> unsigned int token = LOCK_TOKEN;
>
> + if (mmu_has_feature(MMU_FTR_LOCKLESS_TLBIE))
> + return 1;
> +
> asm volatile("1:lwarx %1,0,%2\n"
> " cmpwi cr0,%1,0\n"
> " bne 2f\n"
> @@ -452,6 +455,12 @@ static inline int try_lock_tlbie(unsigned int *lock)
> return old == 0;
> }
>
> +static inline void unlock_tlbie_after_sync(unsigned int *lock)
> +{
> + if (mmu_has_feature(MMU_FTR_LOCKLESS_TLBIE))
> + return;
> +}
> +
> static void do_tlbies(struct kvm *kvm, unsigned long *rbvalues,
> long npages, int global, bool need_sync)
> {
> @@ -483,7 +492,7 @@ static void do_tlbies(struct kvm *kvm, unsigned long *rbvalues,
> }
>
> asm volatile("eieio; tlbsync; ptesync" : : : "memory");
> - kvm->arch.tlbie_lock = 0;
> + unlock_tlbie_after_sync(&kvm->arch.tlbie_lock);
Well that's a silly bug in the !LOCKLESS path, that was supposed
to move to unlock, of course. Will fix it up after some time for
comments.
Thanks,
Nick
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