On Fri, Sep 25, 2015 at 06:18:50PM +0200, 'Klaus Aehlig' via ganeti-devel wrote:
The doShrink function, which is used for tieredAllocation,
tries to find the first shrinking size where the allocation
statistics changes. As computing the allocation statistics
is an expensive operation, use a guess and verify strategy
to do this computation less often.
While there, also fix a typo in the function description.
Signed-off-by: Klaus Aehlig <[email protected]>
---
src/Ganeti/HTools/Cluster.hs | 20 ++++++++++++++------
1 file changed, 14 insertions(+), 6 deletions(-)
diff --git a/src/Ganeti/HTools/Cluster.hs b/src/Ganeti/HTools/Cluster.hs
index 2ea3580..65746fd 100644
--- a/src/Ganeti/HTools/Cluster.hs
+++ b/src/Ganeti/HTools/Cluster.hs
@@ -882,7 +882,7 @@ underlyingCause x = x
-- this resource changes. Note that it might no be possible to allocate
-- an instance at this size; nevertheless there might be a need to change
-- the resource to shrink on, e.g., if the current instance is too big on
--- to resources.
+-- two resources.
doShrink :: (Instance.Instance -> AllocSolution) -> Instance.Instance
-> FailMode -> Maybe Instance.Instance
doShrink allocFn inst fm =
@@ -890,11 +890,19 @@ doShrink allocFn inst fm =
getCount = runListHead 0 snd . filter ((==) physRes . fst)
. collapseFailures . map underlyingCause . asFailures
initialStat = getCount $ allocFn inst
- in case dropWhile ((==) initialStat . getCount . fst)
- . map (allocFn &&& id)
- $ iterateOk (`Instance.shrinkByType` physRes) inst
- of x:_ -> Just $ snd x
- _ -> Nothing
+ hasChanged = ((/=) initialStat . getCount . fst)
+ -- as the list of possible shrinks can be quite long, and, moreover,
+ -- has some cost of computing it, our heuristics is to look into it
+ -- only for a limited range; only once the list is shorter, we do
+ -- binary search.
+ lookAhead = 50
+ heuristics xs = if null (drop lookAhead xs)
+ then length xs `div` 2
+ else lookAhead
+ in fmap snd
+ . monotoneFind heuristics hasChanged
+ . map (allocFn &&& id)
+ $ iterateOk (`Instance.shrinkByType` physRes) inst
-- | Tiered allocation method.
--
--
2.6.0.rc2.230.g3dd15c0
LGTM, thanks
