Some of the statistics values exported by KVM are always only 0 or 1.
It can be useful to export this fact to userspace so that it can track
them specially (for example by polling the value every now and then to
compute a % of time spent in a specific state).
Therefore, add "boolean value" as a new "unit". While it is not exactly
a unit, it walks and quacks like one. In particular, using the type
would be wrong because boolean values could be instantaneous or peak
values (e.g. "is the rmap allocated?") or even two-bucket histograms
(e.g. "number of posted vs. non-posted interrupt injections").
Suggested-by: Amneesh Singh <natto@xxxxxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 6 ++++++
arch/x86/kvm/x86.c | 2 +-
include/linux/kvm_host.h | 11 ++++++++++-
include/uapi/linux/kvm.h | 1 +
4 files changed, 18 insertions(+), 2 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 11e00a46c610..48bf6e49a7de 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -5657,6 +5657,7 @@ by a string of size ``name_size``.
#define KVM_STATS_UNIT_BYTES (0x1 << KVM_STATS_UNIT_SHIFT)
#define KVM_STATS_UNIT_SECONDS (0x2 << KVM_STATS_UNIT_SHIFT)
#define KVM_STATS_UNIT_CYCLES (0x3 << KVM_STATS_UNIT_SHIFT)
+ #define KVM_STATS_UNIT_BOOLEAN (0x4 << KVM_STATS_UNIT_SHIFT)
#define KVM_STATS_UNIT_MAX KVM_STATS_UNIT_CYCLES
#define KVM_STATS_BASE_SHIFT 8
@@ -5724,6 +5725,11 @@ Bits 4-7 of ``flags`` encode the unit:
It indicates that the statistics data is used to measure time or latency.
* ``KVM_STATS_UNIT_CYCLES``
It indicates that the statistics data is used to measure CPU clock cycles.
+ * ``KVM_STATS_UNIT_BOOLEAN``
+ It indicates that the statistic will always be either 0 or 1. Boolean
+ statistics of "peak" type will never go back from 1 to 0. Boolean
+ statistics can be linear histograms (with two buckets) but not logarithmic
+ histograms.
Bits 8-11 of ``flags``, together with ``exponent``, encode the scale of the
unit:
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 26d0cac32f73..0c3e85e8fce9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -298,7 +298,7 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
STATS_DESC_COUNTER(VCPU, directed_yield_successful),
STATS_DESC_COUNTER(VCPU, preemption_reported),
STATS_DESC_COUNTER(VCPU, preemption_other),
- STATS_DESC_ICOUNTER(VCPU, guest_mode)
+ STATS_DESC_IBOOLEAN(VCPU, guest_mode)
};
const struct kvm_stats_header kvm_vcpu_stats_header = {
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 83cf7fd842e0..90a45ef7203b 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1822,6 +1822,15 @@ struct _kvm_stats_desc {
STATS_DESC_PEAK(SCOPE, name, KVM_STATS_UNIT_NONE, \
KVM_STATS_BASE_POW10, 0)
+/* Instantaneous boolean value, read only */
+#define STATS_DESC_IBOOLEAN(SCOPE, name) \
+ STATS_DESC_INSTANT(SCOPE, name, KVM_STATS_UNIT_BOOLEAN, \
+ KVM_STATS_BASE_POW10, 0)
+/* Peak (sticky) boolean value, read/write */
+#define STATS_DESC_PBOOLEAN(SCOPE, name) \
+ STATS_DESC_PEAK(SCOPE, name, KVM_STATS_UNIT_BOOLEAN, \
+ KVM_STATS_BASE_POW10, 0)
+
/* Cumulative time in nanosecond */
#define STATS_DESC_TIME_NSEC(SCOPE, name) \
STATS_DESC_CUMULATIVE(SCOPE, name, KVM_STATS_UNIT_SECONDS, \
@@ -1853,7 +1862,7 @@ struct _kvm_stats_desc {
HALT_POLL_HIST_COUNT), \
STATS_DESC_LOGHIST_TIME_NSEC(VCPU_GENERIC, halt_wait_hist, \
HALT_POLL_HIST_COUNT), \
- STATS_DESC_ICOUNTER(VCPU_GENERIC, blocking)
+ STATS_DESC_IBOOLEAN(VCPU_GENERIC, blocking)
extern struct dentry *kvm_debugfs_dir;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 5088bd9f1922..811897dadcae 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -2083,6 +2083,7 @@ struct kvm_stats_header {
#define KVM_STATS_UNIT_BYTES (0x1 << KVM_STATS_UNIT_SHIFT)
#define KVM_STATS_UNIT_SECONDS (0x2 << KVM_STATS_UNIT_SHIFT)
#define KVM_STATS_UNIT_CYCLES (0x3 << KVM_STATS_UNIT_SHIFT)
+#define KVM_STATS_UNIT_BOOLEAN (0x4 << KVM_STATS_UNIT_SHIFT)
#define KVM_STATS_UNIT_MAX KVM_STATS_UNIT_CYCLES
#define KVM_STATS_BASE_SHIFT 8
--
2.31.1
