Messages in this thread | | | From | Paul Turner <> | Date | Mon, 16 May 2011 05:32:31 -0700 | Subject | Re: [patch 04/15] sched: validate CFS quota hierarchies |
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On Mon, May 16, 2011 at 2:43 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > > On Tue, 2011-05-03 at 02:28 -0700, Paul Turner wrote: > > This behavior may be disabled (allowing child bandwidth to exceed parent) via > > kernel.sched_cfs_bandwidth_consistent=0 > > why? this needs very good justification.
I think it was lost in other discussion before, but I think there are two useful use-cases for it:
Posting (condensed) relevant snippet: ----------------------------------------------------------- Consider:
- I have some application that I want to limit to 3 cpus I have a 2 workers in that application, across a period I would like those workers to use a maximum of say 2.5 cpus each (suppose they serve some sort of co-processor request per user and we want to prevent a single user eating our entire limit and starving out everything else).
The goal in this case is not preventing increasing availability within a given limit, while not destroying the (relatively) work-conserving aspect of its performance in general.
(...)
- There's also the case of managing an abusive user, use cases such as the above means that users can usefully be given write permission to their relevant sub-hierarchy.
If the system size changes, or a user becomes newly abusive then being able to set non-conformant constraint avoids the adversarial problem of having to find and bring all of their set (possibly maliciously large) limits within the global limit. ----------------------------------------------------------- (Previously: https://lkml.org/lkml/2011/2/24/477)
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