Balbir Singh wrote:
How, it works out fine in my calculation
50 + 40 for G2 and G3, make sure that G1 gets 10%, since others are
limited to 90%
50 + 40 for G1 and G3, make sure that G2 gets 10%, since others are
limited to 90%
50 + 50 for G1 and G2, make sure that G3 gets 0%, since others are
limited to 100%
It's fine in that it satisfies the guarantees, but it is deeply
suboptimal. If I ran a cpu hog in the first group, while the other two
were idle, it would be limited to 50% cpu. On the other hand, if it
consumed all 100% cpu it would still satisfy the guarantees (as the
other groups are idle).
The result is that in such a situation, wall clock time would double
even though cpu resources are available.
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?
Suppose in my example cgroup 1 consumed 100% of the cpu resources and
cgroup 2 and 3 were completely idle. All of the guarantees are met (if
cgroup 2 is idle, there's no need to give it the 10% cpu time it is
guaranteed).
If your only tool to achieve the guarantees is a limit system, then
yes, the equation yields the correct results. But given that it yields
such inferior results, I think we need to look for a more involved solution.
I think the limits method fits cases where it is difficult to evict a
resource (say, disk quotas -- if you want to guarantee 10% of space to
cgroups 1, you must limit all others to 90%). But for processor usage,
you can evict a cgroup instantly, so nothing prevents a cgroup from
consuming all available resources as long as others do not contend for them.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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