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    SubjectRe: [PATCH] O13int for interactivity

    Mike Galbraith wrote:

    > At 12:51 PM 8/12/2003 +1000, Nick Piggin wrote:
    >> Rob Landley wrote:
    >>> On Tuesday 05 August 2003 06:32, Nick Piggin wrote:
    >>>> But by employing the kernel's services in the shape of a blocking
    >>>> syscall, all sleeps are intentional.
    >>> Wrong. Some sleeps indicate "I have run out of stuff to do right
    >>> now, I'm going to wait for a timer or another process or something
    >>> to wake me up with new work".
    >>> Some sleeps indicate "ideally this would run on an enormous ramdisk
    >>> attached to gigabit ethernet, but hard drives and internet
    >>> connections are just too slow so my true CPU-hogness is hidden by
    >>> the fact I'm running on a PC instead of a mainframe."
    >> I don't quite understand what you are getting at, but if you don't
    >> want to
    >> sleep you should be able to use a non blocking syscall. But in some
    >> cases
    >> I think there are times when you may not be able to use a non
    >> blocking call.
    >> And if a process is a CPU hog, its a CPU hog. If its not its not.
    >> Doesn't
    >> matter how it would behave on another system.
    > Ah, but there is something there. Take the X and xmms's gl thread
    > thingy I posted a while back. (X runs long enough to expire in the
    > presence of a couple of low priority cpu hogs. gl thread, which is a
    > mondo cpu hog, and normally runs and runs and runs at cpu hog
    > priority, suddenly acquires extreme interactive priority, and X, which
    > is normally sleepy suddenly becomes permanently runnable at cpu hog
    > priority) The gl thread starts sleeping because X isn't getting
    > enough cpu to be able to get it's work done and go to sleep. The gl
    > thread isn't voluntarily sleeping, and X isn't voluntarily running.
    > The behavior change is forced upon both.

    It does... It is I tell ya!

    Look, the gl thread is probably _very_ explicitly asking to sleep. No I
    don't know how X works, but I have an idea that select is generally used
    as an event notification, right?

    Now the gl thread is essentially saying "wait until X finishes the work
    I've given it, or I get some other event": ie. "put me to sleep until
    this fd becomes readable".

    OK maybe your scenario is a big problem. Its not due to any imagined
    semantics in the way things are sleeping. Its due to the scheduler.

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