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>

3 files changed, 3 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 98eebbf66340..195886a583ba 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/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;
diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index d75bf325f54a..cf009167d208 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/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) },
diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
index ae458f0fd061..fd5875179e5c 100644
--- a/arch/powerpc/kvm/booke.c
+++ b/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) },