Change in vdsm[master]: migrations: change migration parameters

michal.skrivanek at redhat.com michal.skrivanek at redhat.com
Wed Apr 6 09:52:32 UTC 2016


Michal Skrivanek has posted comments on this change.

Change subject: migrations: change migration parameters
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Patch Set 2:

we're testing that a bit more with mpolednik. so far the best values seem to be:
concurrency 2
bandwidth 52
stalling 240
downtime_delay 20
downtime steps 5

why? 
1Gb network, with 2 migrations should occupy 832Mbps, practically the line can handle ~880Mbps, so we have a 50Mbps buffer even in the worst case
stalling - 150 was very often not enough. rasising from 2.5 minute to 4 might significantly help to overcome peaks in memory usage, but still conservative enough.
downtime - 10 steps with 75s per GB is too much. theoretically you need less than 20s at 52MB/s on 1Gb line to transfer everything. In reality there are zero pages costing nothing, and dirty memory on the other hand. So roughly 20s to get through one full pass is enough, then it makes sense to tweak downtime. 
The algorithm is not ideal either, so 10->5 means it's going to increase sooner

what do you think?

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Gerrit-MessageType: comment
Gerrit-Change-Id: I1ed1b04ee77a7144ae0206e5c5ae1426ede0c75f
Gerrit-PatchSet: 2
Gerrit-Project: vdsm
Gerrit-Branch: master
Gerrit-Owner: Tomas Jelinek <tjelinek at redhat.com>
Gerrit-Reviewer: Dan Kenigsberg <danken at redhat.com>
Gerrit-Reviewer: Francesco Romani <fromani at redhat.com>
Gerrit-Reviewer: Jenkins CI
Gerrit-Reviewer: Michal Skrivanek <michal.skrivanek at redhat.com>
Gerrit-Reviewer: Tomas Jelinek <tjelinek at redhat.com>
Gerrit-Reviewer: gerrit-hooks <automation at ovirt.org>
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