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KVM: use cpu_relax when halt polling

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SMT siblings share caches and other hardware, and busy halt polling
will degrade its sibling performance if its sibling is working

Sean Christopherson suggested as below:

"Rather than disallowing halt-polling entirely, on x86 it should be
sufficient to simply have the hardware thread yield to its sibling(s)
via PAUSE.  It probably won't get back all performance, but I would
expect it to be close.
This compiles on all KVM architectures, and AFAICT the intended usage
of cpu_relax() is identical for all architectures."

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Message-Id: <20210727111247.55510-1-lirongqing@baidu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Li RongQing 2021-07-27 19:12:47 +08:00 committed by Paolo Bonzini
parent 5868b8225e
commit 7477565433
1 changed files with 1 additions and 0 deletions
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1
virt/kvm/kvm_main.c
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@ -3110,6 +3110,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
++vcpu->stat.generic.halt_poll_invalid;
goto out;
}
cpu_relax();
poll_end = cur = ktime_get();
} while (kvm_vcpu_can_poll(cur, stop));
}