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    SubjectRe: Time sliced CFQ io scheduler
    On Thu, Dec 02, 2004 at 08:52:36PM +0100, Jens Axboe wrote:
    > with its default io scheduler has basically zero write performance in

    IMHO the default io scheduler should be changed to cfq. as is all but
    general purpose so it's a mistake to leave it the default (plus as Jens
    found the write bandwidth is not existent during reads, no surprise it
    falls apart in any database load). We had to make the cfq the default
    for the enterprise release already. The first thing I do is to add
    elevator=cfq on a new install. I really like how well cfq has been
    designed, implemented and turned, Jens's results with his last patch are
    quite impressive.

    BTW, a bit of historic that may be funny to read (and I believe nobody
    on l-k knows about it): the first sfq I/O elevator idea (sfq is the
    ancestor of cfq, cfq still fallbacks in sfq mode in the unlikely case
    that no atomic memory is available during I/O) started at an openmosix
    conference in Bologna, when I was listening to one guy fixing the
    latency of some videogame app migrating from server to server with
    openmosix. So they could use a few boxes clustered to host some hundred
    videogames servers migrating depending the the load (I recall they said
    the users tend to move from one game to the other all at the same time).
    I never heard of sfq before, but when I understood how it worked for the
    packet scheduler and how they were using it to fix a latency issue in
    the responsiveness of their game while the server was migrating, I
    immediatly got the idea I could use the very same sfq algorightm for the
    disk elevator too (at that time it was being used only in the networking
    qdisc packet scheduler). I wasn't really sure at first if it would work
    equally well for disk too (network pays nothing for seeks). But
    conceptually it did worth mentioning the idea to Jens so he could
    evaluate it (I think he was already working on something similar but I
    hope I did provide him with some useful hint). You know the rest, he
    quickly turned it into a cfq and did numerous improvements. The funny
    thing I meant to say, is that if I didn't incidentally listen to the
    videogame talk (a talk I'd normally avoid) we wouldn't have cfq today in
    the I/O scheduler in its current great status (of course we could have
    it since Jens was already working on something similar, but perhaps it
    would be at least a bit in the past compared to his current great

    Even a videogame server may turn out to be very useful ;). I'm quite
    sure the developer doing the videogame openmosix speech doesn't know his
    speech had an impact on the kernel I/O scheduler ;). Hope he reads this
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