KVM: stats: Add halt polling related histogram stats

Add three log histogram stats to record the distribution of time spent
on successful polling, failed polling and VCPU wait.
halt_poll_success_hist: Distribution of spent time for a successful poll.
halt_poll_fail_hist: Distribution of spent time for a failed poll.
halt_wait_hist: Distribution of time a VCPU has spent on waiting.
Signed-off-by: Jing Zhang <jingzhangos@google.com>
Message-Id: <20210802165633.1866976-6-jingzhangos@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/powerpc/kvm/book3s_hv.c

@@ -4146,17 +4146,29 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
 	if (do_sleep) {
 		vc->runner->stat.generic.halt_wait_ns +=
 			ktime_to_ns(cur) - ktime_to_ns(start_wait);
+		KVM_STATS_LOG_HIST_UPDATE(
+				vc->runner->stat.generic.halt_wait_hist,
+				ktime_to_ns(cur) - ktime_to_ns(start_wait));
 		/* Attribute failed poll time */
-		if (vc->halt_poll_ns)
+		if (vc->halt_poll_ns) {
 			vc->runner->stat.generic.halt_poll_fail_ns +=
 				ktime_to_ns(start_wait) -
 				ktime_to_ns(start_poll);
+			KVM_STATS_LOG_HIST_UPDATE(
+				vc->runner->stat.generic.halt_poll_fail_hist,
+				ktime_to_ns(start_wait) -
+				ktime_to_ns(start_poll));
+		}
 	} else {
 		/* Attribute successful poll time */
-		if (vc->halt_poll_ns)
+		if (vc->halt_poll_ns) {
 			vc->runner->stat.generic.halt_poll_success_ns +=
 				ktime_to_ns(cur) -
 				ktime_to_ns(start_poll);
+			KVM_STATS_LOG_HIST_UPDATE(
+				vc->runner->stat.generic.halt_poll_success_hist,
+				ktime_to_ns(cur) - ktime_to_ns(start_poll));
+		}
 	}
 
 	/* Adjust poll time */

include/linux/kvm_host.h

@@ -1453,7 +1453,13 @@ struct _kvm_stats_desc {
 	STATS_DESC_COUNTER(VCPU_GENERIC, halt_wakeup),			       \
 	STATS_DESC_TIME_NSEC(VCPU_GENERIC, halt_poll_success_ns),	       \
 	STATS_DESC_TIME_NSEC(VCPU_GENERIC, halt_poll_fail_ns),		       \
-	STATS_DESC_TIME_NSEC(VCPU_GENERIC, halt_wait_ns)
+	STATS_DESC_TIME_NSEC(VCPU_GENERIC, halt_wait_ns),		       \
+	STATS_DESC_LOGHIST_TIME_NSEC(VCPU_GENERIC, halt_poll_success_hist,     \
+			HALT_POLL_HIST_COUNT),				       \
+	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)
 
 extern struct dentry *kvm_debugfs_dir;
 

include/linux/kvm_types.h

@@ -76,6 +76,8 @@ struct kvm_mmu_memory_cache {
 };
 #endif
 
+#define HALT_POLL_HIST_COUNT			32
+
 struct kvm_vm_stat_generic {
 	u64 remote_tlb_flush;
 };
@@ -88,6 +90,9 @@ struct kvm_vcpu_stat_generic {
 	u64 halt_poll_success_ns;
 	u64 halt_poll_fail_ns;
 	u64 halt_wait_ns;
+	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];
 };
 
 #define KVM_STATS_NAME_SIZE	48

virt/kvm/kvm_main.c

@@ -3222,13 +3222,23 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
 				++vcpu->stat.generic.halt_successful_poll;
 				if (!vcpu_valid_wakeup(vcpu))
 					++vcpu->stat.generic.halt_poll_invalid;
+
+				KVM_STATS_LOG_HIST_UPDATE(
+				      vcpu->stat.generic.halt_poll_success_hist,
+				      ktime_to_ns(ktime_get()) -
+				      ktime_to_ns(start));
 				goto out;
 			}
 			cpu_relax();
 			poll_end = cur = ktime_get();
 		} while (kvm_vcpu_can_poll(cur, stop));
+
+		KVM_STATS_LOG_HIST_UPDATE(
+				vcpu->stat.generic.halt_poll_fail_hist,
+				ktime_to_ns(ktime_get()) - ktime_to_ns(start));
 	}
 
+
 	prepare_to_rcuwait(&vcpu->wait);
 	for (;;) {
 		set_current_state(TASK_INTERRUPTIBLE);
@@ -3244,6 +3254,8 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
 	if (waited) {
 		vcpu->stat.generic.halt_wait_ns +=
 			ktime_to_ns(cur) - ktime_to_ns(poll_end);
+		KVM_STATS_LOG_HIST_UPDATE(vcpu->stat.generic.halt_wait_hist,
+				ktime_to_ns(cur) - ktime_to_ns(poll_end));
 	}
 out:
 	kvm_arch_vcpu_unblocking(vcpu);