linux-kernel - [PATCH v2 15/43] KVM: stats: Add stat to detect if vcpu is currently blocking

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Message-Id: <20211009021236.4122790-16-seanjc@google.com>
Date:   Fri,  8 Oct 2021 19:12:08 -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>,
        Anup Patel <anup.patel@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        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>,
        Atish Patra <atish.patra@....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, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        David Matlack <dmatlack@...gle.com>,
        Oliver Upton <oupton@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>
Subject: [PATCH v2 15/43] 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 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@...gle.com>
Suggested-by: Sean Christopherson <seanjc@...gle.com>
Reviewed-by: David Matlack <dmatlack@...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       | 4 ++++
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 2d837e06eeec..bdaa0e70b060 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1462,7 +1462,8 @@ 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 42894ff7c474..a36ccdc93a72 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3211,6 +3211,8 @@ 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);
@@ -3227,6 +3229,8 @@ bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
 
 	kvm_arch_vcpu_unblocking(vcpu);
 
+	vcpu->stat.generic.blocking = 0;
+
 	return waited;
 }
 
-- 
2.33.0.882.g93a45727a2-goog