Re: 2.6.8-rc1-np1

From: Martin Schlemmer (azarah_at_nosferatu.za.org)
Date: 07/17/04

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    To: Nick Piggin <nickpiggin@yahoo.com.au>
Date:	Sat, 17 Jul 2004 22:52:32 +0200

    On Sat, 2004-07-17 at 11:25, Nick Piggin wrote:
    > Felipe Alfaro Solana wrote:
    > > On Sat, 2004-07-17 at 15:23 +1000, Nick Piggin wrote:
    > >
    > >
    > >>Scheduler behaviour is generally pretty good now so I've increased the
    > >>timeslice size to see how far I can push it. Some workloads really demand
    > >>small timeslices though, so I've added /proc/sys/kernel/base_timeslice.
    > >>If you have any problems with the default, please report it to me, and
    > >>check if lowering this value helps.
    > >
    > >
    > > On my 700Mhz Pentium III Mobile laptop, I feel that 256ms is too high
    > > for the system to keep interactive when a CPU hog is running. For
    >
    > Yeah, it is probably a bit too large here too. A burst of activity
    > from X can cause xmms to skip slightly. Probably 128 or 64 would
    > be a decent default.
    >

    Feels fine here on 3GHz P4 (HT system on i875 with dual channel
    memory, striped raid ST38013AS HDD's). xmms haven't skipped yet
    (X reniced to -10) and desktop switching is quick. First time
    typing might be a bit sluggish in gnome-terminal, but second/third
    char is fine, and vim seems to load fast enough. All this is
    with a 'make -j24' for kernel (yeah, not really that realistic,
    but thought I should give it a go) and make -j4 for xorg-x11 going.
    A few load values is:

    load average: 26.72, 15.99, 7.35
    load average: 27.93, 19.48, 9.52
    load average: 28.02, 19.64, 9.63
    load average: 26.01, 19.36, 9.59

    base_timeslice is 256 btw ...

    > > example, running "while true; do a=2; done" makes the system pretty
    > > sluggish with the default timeslice. This is noticeable while dragging
    > > windows around (the movement is jerky and doesn't feel smooth).
    > > Decreasing the timeslie to 50ms, or even better, 25ms, makes the system
    > > behave much much better, although it will decrease throughput
    > > considerably, I guess.
    > >
    >

    Cannot say I can really feel this test. That with 'make -j4' for
    X have load:

    load average: 2.74, 4.45, 5.98

    where the last is still high from the make -j24.

    > It usually isn't too bad for desktops, but is more important on
    > systems with more CPUs and bigger caches.
    >
    > On this dual P3 with 256K L2 cache, a make -j8 vmlinux uses
    > 162.16user 15.43system, ~150ctxsw/s with base_timeslice = 10000
    > 163.88user 16.16system, ~300ctxsw/s with base_timeslice = 32
    > 192.65user 17.27system, ~1300ctxsw/s with base_timeslice = 1
    >
    > So you come to the point of diminishing returns very quickly, and
    > 32 or even 16 or 8 are probably fine values for a desktop system
    > and worth the small cost for CPU intensive tasks.
    > -
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    -- 
Martin Schlemmer

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