Commit 34bf08a2 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
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KVM: PPC: Book3S HV P9: Reduce mftb per guest entry/exit 



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: default avatarNicholas Piggin <npiggin@gmail.com>
Reviewed-by: default avatarFabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-7-npiggin@gmail.com
parent 9581991a

arch/powerpc/kvm/book3s_hv.c

+2 −2
Original line number Diff line number Diff line
@@ -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);

arch/powerpc/kvm/book3s_hv_p9_entry.c

+3 −2
Original line number Diff line number Diff line
@@ -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))