In the case of histogram statistics, the values are always sample
counts; the unit instead applies to the bucket range. For example,
halt_poll_success_hist is a nanosecond statistic because the buckets are
for 0ns, 1ns, 2-3ns, 4-7ns etc. There isn't really any other sensible
interpretation, but clarify this anyway in the Documentation.
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 48bf6e49a7de..6e090fb96a0e 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -5703,14 +5703,13 @@ Bits 0-3 of ``flags`` encode the type:
by the ``hist_param`` field. The range of the Nth bucket (1 <= N < ``size``)
is [``hist_param``*(N-1), ``hist_param``*N), while the range of the last
bucket is [``hist_param``*(``size``-1), +INF). (+INF means positive infinity
- value.) The bucket value indicates how many samples fell in the bucket's range.
+ value.)
* ``KVM_STATS_TYPE_LOG_HIST``
The statistic is reported as a logarithmic histogram. The number of
buckets is specified by the ``size`` field. The range of the first bucket is
[0, 1), while the range of the last bucket is [pow(2, ``size``-2), +INF).
Otherwise, The Nth bucket (1 < N < ``size``) covers
- [pow(2, N-2), pow(2, N-1)). The bucket value indicates how many samples fell
- in the bucket's range.
+ [pow(2, N-2), pow(2, N-1)).
Bits 4-7 of ``flags`` encode the unit:
@@ -5731,6 +5730,10 @@ Bits 4-7 of ``flags`` encode the unit:
statistics can be linear histograms (with two buckets) but not logarithmic
histograms.
+Note that, in the case of histograms, the unit applies to the bucket
+ranges, while the bucket value indicates how many samples fell in the
+bucket's range.
+
Bits 8-11 of ``flags``, together with ``exponent``, encode the scale of the
unit:
@@ -5752,7 +5755,7 @@ the corresponding statistics data.
The ``bucket_size`` field is used as a parameter for histogram statistics data.
It is only used by linear histogram statistics data, specifying the size of a
-bucket.
+bucket in the unit expressed by bits 4-11 of ``flags`` together with ``exponent``.
The ``name`` field is the name string of the statistics data. The name string
starts at the end of ``struct kvm_stats_desc``. The maximum length including
--
2.31.1
