KVM: add halt_attempted_poll to VCPU stats

This new statistic can help diagnosing VCPUs that, for any reason,
trigger bad behavior of halt_poll_ns autotuning.

For example, say halt_poll_ns = 480000, and wakeups are spaced exactly
like 479us, 481us, 479us, 481us. Then KVM always fails polling and wastes
10+20+40+80+160+320+480 = 1110 microseconds out of every
479+481+479+481+479+481+479 = 3359 microseconds. The VCPU then
is consuming about 30% more CPU than it would use without
polling.  This would show as an abnormally high number of
attempted polling compared to the successful polls.

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com<
Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/arm/include/asm/kvm_host.h

@@ -148,6 +148,7 @@ struct kvm_vm_stat {
 
 struct kvm_vcpu_stat {
 	u32 halt_successful_poll;
+	u32 halt_attempted_poll;
 	u32 halt_wakeup;
 };
 

arch/arm64/include/asm/kvm_host.h

@@ -195,6 +195,7 @@ struct kvm_vm_stat {
 
 struct kvm_vcpu_stat {
 	u32 halt_successful_poll;
+	u32 halt_attempted_poll;
 	u32 halt_wakeup;
 };
 

arch/mips/include/asm/kvm_host.h

@@ -128,6 +128,7 @@ struct kvm_vcpu_stat {
 	u32 msa_disabled_exits;
 	u32 flush_dcache_exits;
 	u32 halt_successful_poll;
+	u32 halt_attempted_poll;
 	u32 halt_wakeup;
 };
 

arch/mips/kvm/mips.c

@@ -55,6 +55,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
 	{ "msa_disabled", VCPU_STAT(msa_disabled_exits), KVM_STAT_VCPU },
 	{ "flush_dcache", VCPU_STAT(flush_dcache_exits), KVM_STAT_VCPU },
 	{ "halt_successful_poll", VCPU_STAT(halt_successful_poll), KVM_STAT_VCPU },
+	{ "halt_attempted_poll", VCPU_STAT(halt_attempted_poll), KVM_STAT_VCPU },
 	{ "halt_wakeup",  VCPU_STAT(halt_wakeup),	 KVM_STAT_VCPU },
 	{NULL}
 };

arch/powerpc/include/asm/kvm_host.h

@@ -108,6 +108,7 @@ struct kvm_vcpu_stat {
 	u32 dec_exits;
 	u32 ext_intr_exits;
 	u32 halt_successful_poll;
+	u32 halt_attempted_poll;
 	u32 halt_wakeup;
 	u32 dbell_exits;
 	u32 gdbell_exits;

arch/powerpc/kvm/book3s.c

@@ -53,6 +53,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
 	{ "ext_intr",    VCPU_STAT(ext_intr_exits) },
 	{ "queue_intr",  VCPU_STAT(queue_intr) },
 	{ "halt_successful_poll", VCPU_STAT(halt_successful_poll), },
+	{ "halt_attempted_poll", VCPU_STAT(halt_attempted_poll), },
 	{ "halt_wakeup", VCPU_STAT(halt_wakeup) },
 	{ "pf_storage",  VCPU_STAT(pf_storage) },
 	{ "sp_storage",  VCPU_STAT(sp_storage) },

arch/powerpc/kvm/booke.c

@@ -63,6 +63,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
 	{ "dec",        VCPU_STAT(dec_exits) },
 	{ "ext_intr",   VCPU_STAT(ext_intr_exits) },
 	{ "halt_successful_poll", VCPU_STAT(halt_successful_poll) },
+	{ "halt_attempted_poll", VCPU_STAT(halt_attempted_poll) },
 	{ "halt_wakeup", VCPU_STAT(halt_wakeup) },
 	{ "doorbell", VCPU_STAT(dbell_exits) },
 	{ "guest doorbell", VCPU_STAT(gdbell_exits) },

arch/s390/include/asm/kvm_host.h

@@ -210,6 +210,7 @@ struct kvm_vcpu_stat {
 	u32 exit_validity;
 	u32 exit_instruction;
 	u32 halt_successful_poll;
+	u32 halt_attempted_poll;
 	u32 halt_wakeup;
 	u32 instruction_lctl;
 	u32 instruction_lctlg;

arch/s390/kvm/kvm-s390.c

@@ -63,6 +63,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
 	{ "exit_program_interruption", VCPU_STAT(exit_program_interruption) },
 	{ "exit_instr_and_program_int", VCPU_STAT(exit_instr_and_program) },
 	{ "halt_successful_poll", VCPU_STAT(halt_successful_poll) },
+	{ "halt_attempted_poll", VCPU_STAT(halt_attempted_poll) },
 	{ "halt_wakeup", VCPU_STAT(halt_wakeup) },
 	{ "instruction_lctlg", VCPU_STAT(instruction_lctlg) },
 	{ "instruction_lctl", VCPU_STAT(instruction_lctl) },

arch/x86/include/asm/kvm_host.h

@@ -711,6 +711,7 @@ struct kvm_vcpu_stat {
 	u32 nmi_window_exits;
 	u32 halt_exits;
 	u32 halt_successful_poll;
+	u32 halt_attempted_poll;
 	u32 halt_wakeup;
 	u32 request_irq_exits;
 	u32 irq_exits;

arch/x86/kvm/x86.c

@@ -149,6 +149,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
 	{ "nmi_window", VCPU_STAT(nmi_window_exits) },
 	{ "halt_exits", VCPU_STAT(halt_exits) },
 	{ "halt_successful_poll", VCPU_STAT(halt_successful_poll) },
+	{ "halt_attempted_poll", VCPU_STAT(halt_attempted_poll) },
 	{ "halt_wakeup", VCPU_STAT(halt_wakeup) },
 	{ "hypercalls", VCPU_STAT(hypercalls) },
 	{ "request_irq", VCPU_STAT(request_irq_exits) },

virt/kvm/kvm_main.c

@@ -2004,6 +2004,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
 	if (vcpu->halt_poll_ns) {
 		ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns);
 
+		++vcpu->stat.halt_attempted_poll;
 		do {
 			/*
 			 * This sets KVM_REQ_UNHALT if an interrupt