[PATCH v2 19/37] KVM: PPC: Book3S HV P9: Use host timer accounting to avoid decrementer read
From: Nicholas Piggin <npiggin@gmail.com>
Date: 2021-02-25 13:55:23
Subsystem:
kernel virtual machine for powerpc (kvm/powerpc), linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Linus Torvalds
There is no need to save away the host DEC value, as it is derived from the host timer subsystem, which maintains the next timer time. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- arch/powerpc/include/asm/time.h | 5 +++++ arch/powerpc/kvm/book3s_hv.c | 12 ++++++------ 2 files changed, 11 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/include/asm/time.h b/arch/powerpc/include/asm/time.h
index 68d94711811e..0128cd9769bc 100644
--- a/arch/powerpc/include/asm/time.h
+++ b/arch/powerpc/include/asm/time.h@@ -101,6 +101,11 @@ extern void __init time_init(void); DECLARE_PER_CPU(u64, decrementers_next_tb); +static inline u64 timer_get_next_tb(void) +{ + return __this_cpu_read(decrementers_next_tb); +} + /* Convert timebase ticks to nanoseconds */ unsigned long long tb_to_ns(unsigned long long tb_ticks);
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 913582bd848f..735ec40ece86 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c@@ -3631,16 +3631,16 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long host_amr = mfspr(SPRN_AMR); unsigned long host_fscr = mfspr(SPRN_FSCR); s64 dec; - u64 tb; + u64 tb, next_timer; int trap, save_pmu; - dec = mfspr(SPRN_DEC); tb = mftb(); - if (dec < 0) + next_timer = timer_get_next_tb(); + if (tb >= next_timer) return BOOK3S_INTERRUPT_HV_DECREMENTER; - local_paca->kvm_hstate.dec_expires = dec + tb; - if (local_paca->kvm_hstate.dec_expires < time_limit) - time_limit = local_paca->kvm_hstate.dec_expires; + local_paca->kvm_hstate.dec_expires = next_timer; + if (next_timer < time_limit) + time_limit = next_timer; vcpu->arch.ceded = 0;
--
2.23.0