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    SubjectRe: is RSDL an "unfair" scheduler too?
    Willy Tarreau wrote:
    > On Sat, Mar 17, 2007 at 06:32:29PM -0700, Linus Torvalds wrote:
    >
    >> On Sat, 17 Mar 2007, William Lee Irwin III wrote:
    >>
    >>> One issue this raises is prioritizing users on a system, threads within
    >>> processes, jobs within users, etc.
    >>>
    >> Doing some "classing" even by just euid might be a good idea. It would
    >> actually catch X automatically most of the time, because the euid of the X
    >> server is likely to be root, so even for the "trivial" desktop example, it
    >> would kind of automatically mean that X would get about 50% of CPU time
    >> even if you have a hundred user clients, just because that's "fair" by
    >> euid.
    >>
    >
    > Warning: all these ideas seem interesting for desktop, but are definitely
    > not for servers. I found RSDL to be excellent on servers, compared to
    > mainline in which some services are starving under load. I can understand
    > that on the desktop people want some unfairness, and I like the pgrp idea
    > for instance. But this one will certainly fail on servers, or make the
    > admins get grey hair very soon.
    >

    I didn't suggest adding any unfairness! I suggested being fair by
    user/job/process instead of being fair by thread (which is actually
    unfair as it favors multi threaded processes over single threaded
    processes).

    > Maybe we're all discussing the problem because we have reached the point
    > where we need two types of schedulers : one for the desktop and one for
    > the servers. After all, this is already what is proposed with preempt,
    > it would make sense provided they share the same core and avoid ifdefs
    > or unused structure members. Maybe adding OPTIONAL unfairness to RSDL
    > would help some scenarios, but in any case it is important to retain
    > the default fairness it provides.
    >

    I hope not. I think that reducing the timeslice base, combined with
    renicing X all the way to hell should suffice.


    --
    Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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