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KVM: Cap vcpu->halt_poll_ns before halting rather than after

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Cap vcpu->halt_poll_ns based on the max halt polling time just before
halting, rather than after the last halt. This arguably provides better
accuracy if an admin disables halt polling in between halts, although
the improvement is nominal.

A side-effect of this change is that grow_halt_poll_ns() no longer needs
to access vcpu->kvm->max_halt_poll_ns, which will be useful in a future
commit where the max halt polling time can come from the module parameter
halt_poll_ns instead.

Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20221117001657.1067231-2-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
David Matlack 2022-11-16 16:16:55 -08:00 committed by Paolo Bonzini
parent 6d3085e4d8
commit 97b6847ac1
1 changed files with 6 additions and 4 deletions
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10
virt/kvm/kvm_main.c
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@ -3377,9 +3377,6 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
if (val < grow_start)
val = grow_start;
if (val > vcpu->kvm->max_halt_poll_ns)
val = vcpu->kvm->max_halt_poll_ns;
vcpu->halt_poll_ns = val;
out:
trace_kvm_halt_poll_ns_grow(vcpu->vcpu_id, val, old);
@ -3492,11 +3489,16 @@ static inline void update_halt_poll_stats(struct kvm_vcpu *vcpu, ktime_t start,
void kvm_vcpu_halt(struct kvm_vcpu *vcpu)
{
bool halt_poll_allowed = !kvm_arch_no_poll(vcpu);
bool do_halt_poll = halt_poll_allowed && vcpu->halt_poll_ns;
ktime_t start, cur, poll_end;
bool waited = false;
bool do_halt_poll;
u64 halt_ns;
if (vcpu->halt_poll_ns > vcpu->kvm->max_halt_poll_ns)
vcpu->halt_poll_ns = vcpu->kvm->max_halt_poll_ns;
do_halt_poll = halt_poll_allowed && vcpu->halt_poll_ns;
start = cur = poll_end = ktime_get();
if (do_halt_poll) {
ktime_t stop = ktime_add_ns(start, vcpu->halt_poll_ns);