linux-kernel - [PATCH 11/14] KVM: stats: Add stat to detect if vcpu is currently blocking

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Message-Id: <20210925005528.1145584-12-seanjc@google.com>
Date:   Fri, 24 Sep 2021 17:55:25 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Marc Zyngier <maz@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Matlack <dmatlack@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>
Subject: [PATCH 11/14] KVM: stats: Add stat to detect if vcpu is currently blocking

From: Jing Zhang <jingzhangos@...gle.com>

Add a "blocking" stat that userspace can use to detect the case where a
vCPU is not being run because of a 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
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@...gle.com>
Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Jing Zhang <jingzhangos@...gle.com>
[sean: renamed stat to "blocking", massaged changelog]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 include/linux/kvm_host.h  | 3 ++-
 include/linux/kvm_types.h | 1 +
 virt/kvm/kvm_main.c       | 2 ++
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 655c2b24db2d..9bb1972e396a 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1453,7 +1453,8 @@ 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;
 
diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
index 2237abb93ccd..c4f9257bf32d 100644
--- a/include/linux/kvm_types.h
+++ b/include/linux/kvm_types.h
@@ -94,6 +94,7 @@ 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
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fe34457530c2..2980d2b88559 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3208,6 +3208,7 @@ bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
 {
 	bool waited = false;
 
+	vcpu->stat.generic.blocking = 1;
 	kvm_arch_vcpu_blocking(vcpu);
 
 	prepare_to_rcuwait(&vcpu->wait);
@@ -3223,6 +3224,7 @@ bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
 	finish_rcuwait(&vcpu->wait);
 
 	kvm_arch_vcpu_unblocking(vcpu);
+	vcpu->stat.generic.blocking = 0;
 
 	return waited;
 }
-- 
2.33.0.685.g46640cef36-goog