On Wed, Jul 29, 2015 at 06:06:29PM +0200, 'Klaus Aehlig' via ganeti-devel wrote:
The Xen CPU collector keeps old values of instance loads for some
time, even after they have moved away. In this way, we can still
obtain a buest-guess load values for an instance before a new load
value can be established on the new node.
For "replace primary" moves on an instance, however, the instance will
visit 3 nodes in short succession. Therefore, keeping old data only
for the time it takes to establish a new load on one node is not
necessarily enough; the instance could be on the intermediate node for
too short to establish a stable load value there. The theoretical
minimum would be 2 times the threshold for accepting load data as
stable; however, due to differences in the sampling time, play it safe
and use 3 times this value. Note that balancing will prefer the load
data from the node where the instance resides, whenever available; so
no harm is done to the accuracy by keeping old values a bit longer.
Signed-off-by: Klaus Aehlig <[email protected]>
---
src/Ganeti/DataCollectors/XenCpuLoad.hs | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/src/Ganeti/DataCollectors/XenCpuLoad.hs
b/src/Ganeti/DataCollectors/XenCpuLoad.hs
index 10c39cd..3ced7ad 100644
--- a/src/Ganeti/DataCollectors/XenCpuLoad.hs
+++ b/src/Ganeti/DataCollectors/XenCpuLoad.hs
@@ -143,7 +143,8 @@ dcUpdate maybeCollector = do
combinedValues
withoutOld = Map.filter
(liftA2 (&&) (not . Seq.null)
- $ (>) (fromIntegral $ C.xentopAverageThreshold * 1000000)
+ $ (>) (fromIntegral
+ $ 3 * C.xentopAverageThreshold * 1000000)
. (clockTimeToUSec now -) . clockTimeToUSec
. fst . flip Seq.index 0)
withinRange
--
2.5.0.rc2.392.g76e840b
LGTM
