[PATCH v5 26/48] KVM: PPC: Book3S HV P9: Reduce mftb per guest entry/exit
From: Nicholas Piggin <npiggin@gmail.com>
Date: 2021-04-01 15:15:47
Subsystem:
kernel virtual machine for powerpc (kvm/powerpc), linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Michael Ellerman, Linus Torvalds
mftb is serialising (dispatch next-to-complete) so it is heavy weight for a mfspr. Avoid reading it multiple times in the entry or exit paths. A small number of cycles delay to timers is tolerable. Reviewed-by: Fabiano Rosas <redacted> Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- arch/powerpc/kvm/book3s_hv.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index dc1232d2a198..46f457c3b828 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c@@ -3551,12 +3551,13 @@ static int kvmhv_load_hv_regs_and_go(struct kvm_vcpu *vcpu, u64 time_limit, host_dawrx1 = mfspr(SPRN_DAWRX1); } - hdec = time_limit - mftb(); + tb = mftb(); + hdec = time_limit - tb; if (hdec < 0) return BOOK3S_INTERRUPT_HV_DECREMENTER; if (vc->tb_offset) { - u64 new_tb = mftb() + vc->tb_offset; + u64 new_tb = tb + vc->tb_offset; mtspr(SPRN_TBU40, new_tb); tb = mftb(); if ((tb & 0xffffff) < (new_tb & 0xffffff))
@@ -3754,7 +3755,7 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit, if (!(vcpu->arch.ctrl & 1)) mtspr(SPRN_CTRLT, mfspr(SPRN_CTRLF) & ~1); - mtspr(SPRN_DEC, vcpu->arch.dec_expires - mftb()); + mtspr(SPRN_DEC, vcpu->arch.dec_expires - tb); if (kvmhv_on_pseries()) { /*
@@ -3889,7 +3890,7 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit, vc->in_guest = 0; next_timer = timer_get_next_tb(); - mtspr(SPRN_DEC, next_timer - mftb()); + mtspr(SPRN_DEC, next_timer - tb); mtspr(SPRN_SPRG_VDSO_WRITE, local_paca->sprg_vdso); kvmhv_load_host_pmu();
--
2.23.0