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KVM: stats: Add stat to detect if vcpu is currently blocking

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Add a "blocking" stat that userspace can use to detect the case where a
vCPU is not being run because of an vCPU/guest action, e.g. HLT or WFS on
x86, WFI on arm64, etc...  Current guest/host/halt stats don't show this
well, e.g. if a guest halts for a long period of time then the vCPU could
could appear pathologically blocked due to a host condition, when in
reality the vCPU has been put into a not-runnable state by the guest.

Originally-by: Cannon Matthews <cannonmatthews@google.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Jing Zhang <jingzhangos@google.com>
[sean: renamed stat to "blocking", massaged changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211009021236.4122790-16-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Jing Zhang 2021-10-08 19:12:08 -07:00 committed by Paolo Bonzini
parent fac4268894
commit c3858335c7
3 changed files with 7 additions and 1 deletions
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3
include/linux/kvm_host.h
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@ -1587,7 +1587,8 @@ struct _kvm_stats_desc {
STATS_DESC_LOGHIST_TIME_NSEC(VCPU_GENERIC, halt_poll_fail_hist, \
HALT_POLL_HIST_COUNT), \
STATS_DESC_LOGHIST_TIME_NSEC(VCPU_GENERIC, halt_wait_hist, \
HALT_POLL_HIST_COUNT)
HALT_POLL_HIST_COUNT), \
STATS_DESC_ICOUNTER(VCPU_GENERIC, blocking)
extern struct dentry *kvm_debugfs_dir;

1
include/linux/kvm_types.h
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@ -87,6 +87,7 @@ struct kvm_vcpu_stat_generic {
u64 halt_poll_success_hist[HALT_POLL_HIST_COUNT];
u64 halt_poll_fail_hist[HALT_POLL_HIST_COUNT];
u64 halt_wait_hist[HALT_POLL_HIST_COUNT];
u64 blocking;
};
#define KVM_STATS_NAME_SIZE 48

4
virt/kvm/kvm_main.c
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@ -3282,6 +3282,8 @@ bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
struct rcuwait *wait = kvm_arch_vcpu_get_wait(vcpu);
bool waited = false;
vcpu->stat.generic.blocking = 1;
kvm_arch_vcpu_blocking(vcpu);
prepare_to_rcuwait(wait);
@ -3298,6 +3300,8 @@ bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
kvm_arch_vcpu_unblocking(vcpu);
vcpu->stat.generic.blocking = 0;
return waited;
}