Re: [RFC] CPU hard limits
From: Avi Kivity
Date: Fri Jun 05 2009 - 02:03:52 EST
Bharata B Rao wrote:
On Fri, Jun 05, 2009 at 01:27:55PM +0800, Balbir Singh wrote:
* Avi Kivity <avi@xxxxxxxxxx> [2009-06-05 08:21:43]:
Balbir Singh wrote:
But then there is no other way to make a *guarantee*, guarantees come
at a cost of idling resources, no? Can you show me any other
combination that will provide the guarantee and without idling the
system for the specified guarantees?
OK, I see part of your concern, but I think we could do some
optimizations during design. For example if all groups have reached
their hard-limit and the system is idle, should we do start a new hard
limit interval and restart, so that idleness can be removed. Would
that be an acceptable design point?
I think so. Given guarantees G1..Gn (0 <= Gi <= 1; sum(Gi) <= 1), and a
cpu hog running in each group, how would the algorithm divide resources?
As per the matrix calculation, but as soon as we reach an idle point,
we redistribute the b/w and start a new quantum so to speak, where all
groups are charged up to their hard limits.
But could there be client models where you are required to strictly
adhere to the limit within the bandwidth and not provide more (by advancing
the bandwidth period) in the presence of idle cycles ?
That's the limit part. I'd like to be able to specify limits and
guarantees on the same host and for the same groups; I don't think that
works when you advance the bandwidth period.
I think we need to treat guarantees as first-class goals, not something
derived from limits (in fact I think guarantees are more useful as they
can be used to provide SLAs).
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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