fc2, xorg, 2.6.x, scheduling latency peaks

[Arjan van de Ven]

> In [c] and [d] I'm applying an additional latency patch to the drm
> kernel driver that affects radeon, r128 and mga based cards. The patch
> is old and _illegal_ as it does reschedules with a lock on. So far the
> computer has not locked up but I guess it is a matter of time :-)

can you send me that patch (or point at an URL) ?

> A real test with the Jack low latency server reveals that something else
> is creating latency hits.

do you run Jack as realtime process ??

> So, latencytest is happy but a real test with real applications is not. 
> 

it might be an application artifact/interaction

> Other important data points:
> 
> - xruns seem to be related to graphics activity
> - booting FC2 into 2.4.26 with the low latency and preempt patches gives
> me similar results (latency hits when running jack and jack apps)
> - booting FC1 into 2.4.26 (same hardware, just replace the hard disk)
> gives me a rock solid system (no xruns whatsoever, down to 128x2). 
> 
> So, it would seem to me that it is not (only) the kernel..........
> 
> Things I could not make work:
> - testing 2.6.6-1.391.x in FC1. For some reason init does not get
> executed, probably a library problem somewhere...

you need to pass vdso=0 to the kernel there.


> Any ideas on what could cause this????
> 

try disabling DRI.

DRI sometimes can "hold" the pci bus for quite some time, which by
definition causes latency since no IO can be done

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