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    SubjectRe: [2.4.17/18pre] VM and swap - it's really unusable

    On Tue, 8 Jan 2002, Ken Brownfield wrote:

    > On Wed, Jan 09, 2002 at 12:02:48AM +0100, Luigi Genoni wrote:
    > | Probably sometimes they are not making a good business. In the reality
    > | preempt is good in many scenarios, as I said, and I agree that for
    > | desktops, and dedicated servers where just one application runs, and
    > | probably the CPU is idle the most of the time, indeed users have a speed
    > | feeling. Please consider that on eavilly loaded servers, with 40 and more
    > | users, some are running gcc, others g77, others g++ compilations, someone
    > | runs pine or mutt or kmail, and netscape, and mozilla, and emacs (someone
    > | form xterm kde or gnome), and and
    > | and... You can have also 4/8 CPU butthey are not infinite ;) (but I talk
    > | mainly thinking of dualAthlon systems).
    > | there is a lot of memory and disk I/O.
    > | This is not a strange scenary on the interactive servers used at SNS.
    > | Here preempt has a too high price
    > MacOS 9 is the OS for you.
    > Essentially what the low-latency patches are is cooperative
    > multitasking. Which has less overhead in some cases than preemptive as
    > long as everyone is equally nice and calls WaitNextEvent() within the
    > right inner loops. In the absence of preemptive, Andrew's patch is the
    > next best thing. But Bad Things happen without preemptive. Just try
    > using Mac OS 9 :)
    Not exaclty what I was thinking about.
    I listened some horror story from MAC sysadmin at SNS
    > Preemptive gives better interactivity under load, which is the whole
    > point of multitasking (think about it). If you don't want the overhead
    > (which also exists without preemptive) run #processes == #processors.
    > Whether or not preemptive is applied, having a large number of processes
    > active is a performance hit from context switches, cache thrashing, etc.
    > Preemptive punishes (and rewards) everyone equally, thus better latency.
    you are supposing that I want them to be punished equally. But there are
    cases when that is not what you want ;). Thing if one users runs a
    montecarlo code for test in the server I was describing. This job could
    run, let's say, a couple of hour, and also under nice 20 it can suck a
    > I'm really surprised that people are still actually arguing _against_
    > preemptive multitasking in this day and age. This is a no-brainer in
    > the long run, where current corner cases aren't holding us back.
    > At least IMVHO.
    What I am talking about is some test I did some week ago. The initial post
    of this thread, I think, was very clear about that. On the long run, with
    a very well tested implementation. Actually it is not a good idea to
    insert preempt nside of the 2.4 stable tree,
    because there is a lot of work to do
    to get a very WELL TESTED implementation.

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