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KVM: PPC: Book3S HV P9: Reduce mftb per guest entry/exit

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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.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-7-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2021-11-23 19:51:44 +10:00 committed by Michael Ellerman
parent 9581991a60
commit 34bf08a207
2 changed files with 5 additions and 4 deletions
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4
arch/powerpc/kvm/book3s_hv.c
View File

@ -3940,7 +3940,7 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
*
* XXX: Another day's problem.
*/
mtspr(SPRN_DEC, vcpu->arch.dec_expires - mftb());
mtspr(SPRN_DEC, vcpu->arch.dec_expires - tb);
if (kvmhv_on_pseries()) {
/*
@ -4063,7 +4063,7 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
vc->in_guest = 0;
next_timer = timer_get_next_tb();
set_dec(next_timer - mftb());
set_dec(next_timer - tb);
/* We may have raced with new irq work */
if (test_irq_work_pending())
set_dec(1);

5
arch/powerpc/kvm/book3s_hv_p9_entry.c
View File

@ -203,7 +203,8 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
unsigned long host_dawr1;
unsigned long host_dawrx1;
hdec = time_limit - mftb();
tb = mftb();
hdec = time_limit - tb;
if (hdec < 0)
return BOOK3S_INTERRUPT_HV_DECREMENTER;
@ -215,7 +216,7 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
vcpu->arch.ceded = 0;
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))