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    SubjectRe: [PATCH] hrtimers: Special-case zero length sleeps
    On Wed, 15 Feb 2012, Matthew Garrett wrote:

    > On Wed, Feb 15, 2012 at 09:30:20PM +0100, Thomas Gleixner wrote:
    > > On Wed, 15 Feb 2012, Matthew Garrett wrote:
    > > > Excellent. So the real question is what /should/ sleep(0) do - nothing,
    > > > schedule or sleep for an arbitrary period of time that could be years?
    > >
    > > Well, I don't expect slack to be set to years and I really don't want
    > > to special case sleep(0), because then we might end up discussing
    > > special casing usleep(1) or nanosleep(1ns) as well.
    >
    > Increasing slack to the seconds range has measureable power management
    > benefits, but there's some code that ends up broken as a result even
    > when they're nominally event driven. I've no problem with us just
    > declaring that code as broken, but it would be less effort to special
    > case it. Application authors do seem to have ended up under the belief
    > that sleep(0) is a meaningful thing to do, and the internet seems to be
    > full of suggestions to use it rather than sched_yield().

    The internet is full of crappy suggestions written by absolutely
    clueless and advisory resistant morons.

    Dammit, we cannot come up with a reasonable definition for special
    casing that stuff simply because you cannot draw a clear boundary what
    to special case and what not. And there is no sensible definition for
    what to do - return right away or go through schedule() or what ever.

    sleep(0) is as pointless as sched_yield() and it's about time that we
    stop to create a fucking mess in the kernel just because user space
    programmers refuse to understand how an operating system works and how
    proper programming should be done.

    Thanks,

    tglx


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