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    SubjectRe: [RFC 2/5] sched: Add CPU rate soft caps
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    On Fri, 2006-05-26 at 21:17 +1000, Con Kolivas wrote:
    > On Friday 26 May 2006 21:15, Mike Galbraith wrote:
    > > On Fri, 2006-05-26 at 20:48 +1000, Con Kolivas wrote:
    > > > On Friday 26 May 2006 14:20, Peter Williams wrote:
    > > > > 3. Enforcement of caps is not as strict as it could be in order to
    > > > > reduce the possibility of a task being starved of CPU while holding
    > > > > an important system resource with resultant overall performance
    > > > > degradation. In effect, all runnable capped tasks will get some amount
    > > > > of CPU access every active/expired swap cycle. This will be most
    > > > > apparent for small or zero soft caps.
    > > >
    > > > The array swap happens very frequently if there are nothing but heavily
    > > > cpu bound tasks, which is not an infrequent workload. I doubt the zero
    > > > caps are very effective in that environment.
    > >
    > > Hmm. I think that came out kinda back-assward. You meant "the array
    > > swap happens very frequently _unless_..." No?
    >
    > No I didn't. If all you are doing is compiling code then the array swap will
    > happen often as they will always use up their full timeslice and expire.
    > Therefore an array swap will follow shortly afterwards.

    Afterward being possibly ages. Frequent array switch happens when you
    have mostly sleepy processes, not cpu bound. But whatever.

    > > But anyway, I can't think of any reason to hold back an uncontested
    > > resource.
    >
    > If you are compiling applications it's a contested resource.

    These zero capped tasks are at the bottom of the heap. They won't be
    selected if there's any other runnable task, so it's not contested.

    -Mike

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