Re: [PATCH v1 30/55] KVM: PPC: Book3S HV P9: Only execute mtSPR if the value changed

Nicholas Piggin <[email protected]> writes:

> Keep better track of the current SPR value in places where
> they are to be loaded with a new context, to reduce expensive
> mtSPR operations.
>
> -73 cycles (7354) POWER9 virt-mode NULL hcall
>
> Signed-off-by: Nicholas Piggin <[email protected]>

Reviewed-by: Fabiano Rosas <[email protected]>

> ---
>  arch/powerpc/kvm/book3s_hv.c | 64 ++++++++++++++++++++++--------------
>  1 file changed, 39 insertions(+), 25 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 0d97138e6fa4..56429b53f4dc 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -4009,19 +4009,28 @@ static void switch_pmu_to_host(struct kvm_vcpu *vcpu,
>  	}
>  }
>
> -static void load_spr_state(struct kvm_vcpu *vcpu)
> +static void load_spr_state(struct kvm_vcpu *vcpu,
> +				struct p9_host_os_sprs *host_os_sprs)
>  {
> -	mtspr(SPRN_DSCR, vcpu->arch.dscr);
> -	mtspr(SPRN_IAMR, vcpu->arch.iamr);
> -	mtspr(SPRN_PSPB, vcpu->arch.pspb);
> -	mtspr(SPRN_FSCR, vcpu->arch.fscr);
>  	mtspr(SPRN_TAR, vcpu->arch.tar);
>  	mtspr(SPRN_EBBHR, vcpu->arch.ebbhr);
>  	mtspr(SPRN_EBBRR, vcpu->arch.ebbrr);
>  	mtspr(SPRN_BESCR, vcpu->arch.bescr);
> -	mtspr(SPRN_TIDR, vcpu->arch.tid);
> -	mtspr(SPRN_AMR, vcpu->arch.amr);
> -	mtspr(SPRN_UAMOR, vcpu->arch.uamor);
> +
> +	if (!cpu_has_feature(CPU_FTR_ARCH_31))
> +		mtspr(SPRN_TIDR, vcpu->arch.tid);
> +	if (host_os_sprs->iamr != vcpu->arch.iamr)
> +		mtspr(SPRN_IAMR, vcpu->arch.iamr);
> +	if (host_os_sprs->amr != vcpu->arch.amr)
> +		mtspr(SPRN_AMR, vcpu->arch.amr);
> +	if (vcpu->arch.uamor != 0)
> +		mtspr(SPRN_UAMOR, vcpu->arch.uamor);
> +	if (host_os_sprs->fscr != vcpu->arch.fscr)
> +		mtspr(SPRN_FSCR, vcpu->arch.fscr);
> +	if (host_os_sprs->dscr != vcpu->arch.dscr)
> +		mtspr(SPRN_DSCR, vcpu->arch.dscr);
> +	if (vcpu->arch.pspb != 0)
> +		mtspr(SPRN_PSPB, vcpu->arch.pspb);
>
>  	/*
>  	 * DAR, DSISR, and for nested HV, SPRGs must be set with MSR[RI]
> @@ -4036,28 +4045,31 @@ static void load_spr_state(struct kvm_vcpu *vcpu)
>
>  static void store_spr_state(struct kvm_vcpu *vcpu)
>  {
> -	vcpu->arch.ctrl = mfspr(SPRN_CTRLF);
> -
> -	vcpu->arch.iamr = mfspr(SPRN_IAMR);
> -	vcpu->arch.pspb = mfspr(SPRN_PSPB);
> -	vcpu->arch.fscr = mfspr(SPRN_FSCR);
>  	vcpu->arch.tar = mfspr(SPRN_TAR);
>  	vcpu->arch.ebbhr = mfspr(SPRN_EBBHR);
>  	vcpu->arch.ebbrr = mfspr(SPRN_EBBRR);
>  	vcpu->arch.bescr = mfspr(SPRN_BESCR);
> -	vcpu->arch.tid = mfspr(SPRN_TIDR);
> +
> +	if (!cpu_has_feature(CPU_FTR_ARCH_31))
> +		vcpu->arch.tid = mfspr(SPRN_TIDR);
> +	vcpu->arch.iamr = mfspr(SPRN_IAMR);
>  	vcpu->arch.amr = mfspr(SPRN_AMR);
>  	vcpu->arch.uamor = mfspr(SPRN_UAMOR);
> +	vcpu->arch.fscr = mfspr(SPRN_FSCR);
>  	vcpu->arch.dscr = mfspr(SPRN_DSCR);
> +	vcpu->arch.pspb = mfspr(SPRN_PSPB);
> +
> +	vcpu->arch.ctrl = mfspr(SPRN_CTRLF);
>  }
>
>  static void save_p9_host_os_sprs(struct p9_host_os_sprs *host_os_sprs)
>  {
> -	host_os_sprs->dscr = mfspr(SPRN_DSCR);
> -	host_os_sprs->tidr = mfspr(SPRN_TIDR);
> +	if (!cpu_has_feature(CPU_FTR_ARCH_31))
> +		host_os_sprs->tidr = mfspr(SPRN_TIDR);
>  	host_os_sprs->iamr = mfspr(SPRN_IAMR);
>  	host_os_sprs->amr = mfspr(SPRN_AMR);
>  	host_os_sprs->fscr = mfspr(SPRN_FSCR);
> +	host_os_sprs->dscr = mfspr(SPRN_DSCR);
>  }
>
>  /* vcpu guest regs must already be saved */
> @@ -4066,18 +4078,20 @@ static void restore_p9_host_os_sprs(struct kvm_vcpu *vcpu,
>  {
>  	mtspr(SPRN_SPRG_VDSO_WRITE, local_paca->sprg_vdso);
>
> -	mtspr(SPRN_PSPB, 0);
> -	mtspr(SPRN_UAMOR, 0);
> -
> -	mtspr(SPRN_DSCR, host_os_sprs->dscr);
> -	mtspr(SPRN_TIDR, host_os_sprs->tidr);
> -	mtspr(SPRN_IAMR, host_os_sprs->iamr);
> -
> +	if (!cpu_has_feature(CPU_FTR_ARCH_31))
> +		mtspr(SPRN_TIDR, host_os_sprs->tidr);
> +	if (host_os_sprs->iamr != vcpu->arch.iamr)
> +		mtspr(SPRN_IAMR, host_os_sprs->iamr);
> +	if (vcpu->arch.uamor != 0)
> +		mtspr(SPRN_UAMOR, 0);
>  	if (host_os_sprs->amr != vcpu->arch.amr)
>  		mtspr(SPRN_AMR, host_os_sprs->amr);
> -
>  	if (host_os_sprs->fscr != vcpu->arch.fscr)
>  		mtspr(SPRN_FSCR, host_os_sprs->fscr);
> +	if (host_os_sprs->dscr != vcpu->arch.dscr)
> +		mtspr(SPRN_DSCR, host_os_sprs->dscr);
> +	if (vcpu->arch.pspb != 0)
> +		mtspr(SPRN_PSPB, 0);
>
>  	/* Save guest CTRL register, set runlatch to 1 */
>  	if (!(vcpu->arch.ctrl & 1))
> @@ -4169,7 +4183,7 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
>  #endif
>  	mtspr(SPRN_VRSAVE, vcpu->arch.vrsave);
>
> -	load_spr_state(vcpu);
> +	load_spr_state(vcpu, &host_os_sprs);
>
>  	if (kvmhv_on_pseries()) {
>  		/*