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authorSean Christopherson2021-10-08 19:12:04 -0700
committerPaolo Bonzini2021-12-08 04:24:49 -0500
commitf6c60d081e2ccb4655fa90625b630c860a99d036 (patch)
tree5d79bb5c46daef37785be83055f5d7030107096b /virt
parent6109c5a6ab7f38ed8e1beb06a90aa83884c18700 (diff)
KVM: Don't block+unblock when halt-polling is successful
Invoke the arch hooks for block+unblock if and only if KVM actually attempts to block the vCPU. The only non-nop implementation is on x86, specifically SVM's AVIC, and there is no need to put the AVIC prior to halt-polling; KVM x86's kvm_vcpu_has_events() will scour the full vIRR to find pending IRQs regardless of whether the AVIC is loaded/"running". The primary motivation is to allow future cleanup to split out "block" from "halt", but this is also likely a small performance boost on x86 SVM when halt-polling is successful. Adjust the post-block path to update "cur" after unblocking, i.e. include AVIC load time in halt_wait_ns and halt_wait_hist, so that the behavior is consistent. Moving just the pre-block arch hook would result in only the AVIC put latency being included in the halt_wait stats. There is no obvious evidence that one way or the other is correct, so just ensure KVM is consistent. Note, x86 has two separate paths for handling APICv with respect to vCPU blocking. VMX uses hooks in x86's vcpu_block(), while SVM uses the arch hooks in kvm_vcpu_block(). Prior to this path, the two paths were more or less functionally identical. That is very much not the case after this patch, as the hooks used by VMX _must_ fire before halt-polling. x86's entire mess will be cleaned up in future patches. Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20211009021236.4122790-12-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'virt')
-rw-r--r--virt/kvm/kvm_main.c7
1 files changed, 4 insertions, 3 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 44158a4794d8..cc68d21a8e58 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3306,8 +3306,6 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
bool waited = false;
u64 block_ns;
- kvm_arch_vcpu_blocking(vcpu);
-
start = cur = poll_end = ktime_get();
if (do_halt_poll) {
ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns);
@@ -3324,6 +3322,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
} while (kvm_vcpu_can_poll(cur, stop));
}
+ kvm_arch_vcpu_blocking(vcpu);
prepare_to_rcuwait(wait);
for (;;) {
@@ -3336,6 +3335,9 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
schedule();
}
finish_rcuwait(wait);
+
+ kvm_arch_vcpu_unblocking(vcpu);
+
cur = ktime_get();
if (waited) {
vcpu->stat.generic.halt_wait_ns +=
@@ -3344,7 +3346,6 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
ktime_to_ns(cur) - ktime_to_ns(poll_end));
}
out:
- kvm_arch_vcpu_unblocking(vcpu);
block_ns = ktime_to_ns(cur) - ktime_to_ns(start);
/*