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    SubjectRe: [2.4.17/18pre] VM and swap - it's really unusable
    yodaiken@fsmlabs.com schrieb:
    >
    > On Mon, Jan 21, 2002 at 05:33:50PM +0100, Peter Wächtler wrote:
    > > yodaiken@fsmlabs.com schrieb:
    > > >
    > > > On Mon, Jan 21, 2002 at 05:05:01PM +0100, Daniel Phillips wrote:
    > > > > > I think of "benefit", perhaps naiively, in terms of something that can
    > > > > > be measured or demonstrated rather than just announced.
    > > > >
    > > > > But you see why asap scheduling improves latency/throughput *in theory*,
    > > >
    > > > Nope. And I don't even see a relationship between preemption and asap I/O
    > > > schedulding. What make you think that I/O threads won't be preempted by
    > > > other threads?
    > > >
    > >
    > > I/O intensive threads block early voluntarily - while CPU hogs don't.
    >
    > Since the preemption patch only allows additional preemption in kernel
    > mode, I'm curious to know what the compute bound tasks are doing in
    > kernel mode. Did Linux add in-kernel matrix multiplication while
    > I was not looking?
    >

    Dead right you are.
    Then there are only slow system calls left. Umh, execve(), fork()
    (with big address space) - what about page_launder etc.?


    > > Statistically there is a higher chance, that a CPU hog gets preempted
    > > instead of an IO bound (that gives up the CPU in some useconds anyway)
    >
    > "Statistically"? As far as I know, most I/O in Linux does not block.

    You mean, the syscall returns without a reschedule?
    Aehm, now it's time for some statistics where the kernel spents its time on ;-)

    But what is a possible explanation for the people, who think their
    systems behave better with preemption - strong believe?
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