On Wed, Nov 02, 2016 at 09:13:39PM +0800, Yongji Xie wrote:
> This keeps a per vcpu cache for recently page faulted MMIO entries.
> On a page fault, if the entry exists in the cache, we can avoid
> locking the HPTE in real mode and virtual mode, then directly
> call kvmppc_hv_emulate_mmio().
>
> In current implenment, we limit the size of cache to four. We think
> it's enough to cover the high-frequency MMIO HPTEs in most case.
> For example, considering the case of using virtio device, for virtio
> legacy devices, one HPTE could handle notifications from up to
> 1024 (64K page / 64 byte Port IO register) devices, so one cache entry
> is enough; for virtio modern devices, we always need one HPTE to handle
> notification for each device because modern device would use a 8M MMIO
> register to notify host instead of Port IO register, typically the
> system's configuration should not exceed four virtio devices per
> vcpu, four cache entry is also enough in this case. Of course, if needed,
> we could also modify the macro to a module parameter in the future.
Thanks, the patch looks nice. I did notice one thing though, see below.
Do you have any performance results with and without the patch, to
show the improvement it gives? Something like the throughput for a
1-byte ping-pong message test over virtio-net with vhost, perhaps?
> diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> index 61ff8ee..1f048e7 100644
> --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> @@ -389,6 +389,11 @@ long kvmppc_h_enter(struct kvm_vcpu *vcpu, unsigned long flags,
> #define LOCK_TOKEN (*(u32 *)(&get_paca()->paca_index))
> #endif
>
> +static inline int is_mmio_hpte(unsigned long v, unsigned long r)
> +{
> + return ((v & HPTE_V_ABSENT) && (r & (HPTE_R_KEY_HI | HPTE_R_KEY_LO)));
Shouldn't this be testing (r & (HPTE_R_KEY_HI | HPTE_R_KEY_LO)) ==
(HPTE_R_KEY_HI | HPTE_R_KEY_LO), rather than just a non-zero key field?
Regards,
Paul.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
