Hi Erwin,
I have seen similar latencies with XFree servers when acceleration
is turned on. The problem was traced to PCI bus activity and is not
really interrupt related. Some X server acceleration uses a mode
of the PCI bridge which basically enables an infinite retry sequence.
A command is given to the video chip and then the status is read, the
chip does not respond right away and the PCI bus essentially hangs
while the PCI hardware retries the read until the video chip responds.
This is a particularly nasty featue of the PCI bus and can destroy
determinism in a system which requires real time response. In some
X servers this PCI retry can be turned off while retaining other
acceleration features.
Regards,
Wm
On Tue, 21 Nov 2000, Erwin Rol wrote:
> Hey Paolo,
>
> I don't see it "every" key press , i see it every enter/return key
> press. Which maybe has nothing to do with the keypress , but with the
> scrolling in the terminal window ?
>
> As mentioned in my other mail it works normaly when i disable
> acceleration of the video card.
>
> tonight i will do a serious stress test, to see if it is really stable
> and stays under 50 usec. When that is successful, i will try with a
> other videocard and see if thats causes problems too under XFree 4.0.1
> or if it is just my video card that sucks (which it does :-)
>
>
>
> an other question, is there anyway to figure out if it is caused by
> "lockingup" the PCI-bus , without a logic-analizer or scoop ?
>
> BTW who is eDwin ? :-)
>
> - Erwin
>
>
> Paolo Mantegazza wrote:
> >
> > [EMAIL PROTECTED] wrote:
> > >
> > >
> > > This is possible, however, I suspect that Edwin's problem is not with X.
> > > Before speculating too much, he should see if a big I/O load without X
> > > gets the same behavior.
> > >
> >
> > As I told Edwin, I am not able to reproduce his problem on a PIII 350,
> > UP/MP,
> > by doing the same actions under X, with a looping cp/sync and a ping -f.
> >
> > I tested just for 10 minutes or so with X 3.3.6. Since Edwin's problem
> > is deterministic, he sees it at every keypress, I think it should not be
> > a matter of waiting more time.
> >
> > Ciao, Paolo.
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