Messages in this thread | | | Date | Tue, 21 Dec 2004 10:32:16 -0800 (PST) | From | jesse <> | Subject | Re: Gurus, a silly question for preemptive behavior |
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Con:
thank you for your prompt reply in the holiday season.
My point is: Even kernel 2.4 is not preemptive, the latence should be very minimal.(<300ms) why user space application with low nice priority can't be effectively interrupted and holds the CPU resource since all user space application is preemptive?
Merry Xmas.
jesse
--- Con Kolivas <kernel@kolivas.org> wrote:
> jesse writes: > > > > > As i know, in linux, user space application is > > preemptive at any time. however, linux kernel is > NOT > > preemptive, that means, even some event is > finished, > > Linux kernel scheduler itself still can't have > > opportunity to interrupt the current user > application > > and switch it out. it is called scheduler latency. > > The kernel is preemptible if you enable the preempt > option in the > configuration. There are some code paths that are > not preemptible despite > this, but they are gradually being improved over > time. > > > normally , the latency is about 88us in mean , > maximum > > : 200ms. Thus, the short latency shouldn't impact > user > > applications too much and is not a problem. It is > an > > issue in those embedded voice processing systems > by > > introducing jitters, thus smart people came up > with > > two kernel schedule patch: preemptive patch and > low > > latency patch. > > You're thinking about the 2.4 kernel. 2.6 is > effectively both of those > patches inclusive. > > > my system: > > [root@sa-c2-7 proc]# uname -a > > Linux sa-c2-7 2.4.21-15.ELsmp #1 SMP Thu Apr 22 > > 00:18:24 EDT 2004 i686 i686 i386 GNU/Linux > > If you want lower latency on a 2.4 kernel you need > further patches. You are > most likely to benefit from a move to a 2.6 kernel > and enabling preempt. > > Cheers, > Con > >
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