Messages in this thread |  | | Subject | Re: [PATCH] Preemption Latency Measurement Tool | From | Robert Love <> | Date | 22 Sep 2001 22:58:12 -0400 |
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On Sat, 2001-09-22 at 20:15, safemode wrote: > hrmm strange because the only thing that could be causing the soundcard to > skip would be irq requests still stuck in the cpu as far as i know. I only > get that with massive ide access and that's it. Also that is when linux is > juggling them all equally.
The soundcard will skip whenever there is not enough data for it to play, this would be caused by the mp3 player not getting the needed CPU time (or the PCI bus is saturated or some such).
This could be caused by more than just irq requests -- anytime the kernel can't schedule the mp3 player readily enough. With the preemption patch, this can occur during not just interrupt handling but any concurreny lock.
> > > even i dont get any skips when i run the player at nice -n -20. > > > > During dbench 16/32 and higher? Are you sure? > > I ran it myself and i dont drink alcohol or take drugs. so yea, i'm sure :)
Heh :)
> If i went high enough i suppose the same problem would occur. it's probably > in an area of the kernel where the preempt patch doesn't work (yet). It > does happen on cdparanoia -Z -B "1" I dont think anything ide is safe from > that.
By design, preemption does not occur under any lock (right now we use SMP locks). This means all the spinlocks in the kernel disable preemption, the big kernel lock disables preemption, irq_off obviously does, etc.
What we need to do now is identify the long held locks and -- if they are causing problems -- do something about them.
-- Robert M. Love rml at ufl.edu rml at tech9.net
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