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    SubjectRe: [patch, 2.6.11-rc2] sched: RLIMIT_RT_CPU_RATIO feature
    On Wed, Feb 02, 2005 at 10:21:00PM +0100, Ingo Molnar wrote:
    > yes and no. You are right in that the individual workloads (e.g.
    > softirqs) are not separated and identified/credited to the thread that
    > requested them. (in part due to the fact that you cannot e.g. credit a
    > thread for e.g. unrequested workloads like incoming sockets, or for
    > 'merged' workloads like writeout of a commonly accessed file.)

    What's not being addressed here is a need for pervasive QoS across all
    kernel systems. The power of this patch is multiplicative. It's not
    about a specific component of the system having microsecond latencies,
    it's about how all parts, softirqs, hardirqs, VM, etc... work together
    so that the entire system is suitable for (near) hard real time. It's
    unconstrained, unlike dual kernel RT systems, across all component
    boundaries. Those constraints create large chunks of glue logic between
    systems, which is exploded the complexity of things that app folks
    much deal with.

    This is where properly written Linux apps (non exist right now because
    of kernel issues) can really overtake competing apps from other OSes
    (ignoring how crappy X11 is).

    > but Jack is right in practical terms: the audio folks achieved pretty
    > good results with the current IRQ threading mechanism, partly due to the
    > fact that the audio stack doesnt use softirqs, so all the
    > latency-critical activities are in the audio IRQ thread and the
    > application itself.

    It's clever that they do that, but additional control is needed in the
    future. jackd isn't the most sophisticate media app on this planet (not
    too much of an insult :)) and the demands from this group is bound to
    increase as their group and competing projects get more and more
    sophisticated. When I mean kernel folks needs to be proactive, I really
    mean it. The Linux kernel latency issues and poor driver support is
    largely why media apps are way below even being second rate with regard
    to other operating systems such as Apple's OS X for instance.


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