16 Feb
2013
16 Feb
'13
3:17 p.m.
On Thu, 14 Feb 2013 12:06:06 -0500, Gene Heskett wrote:
On Thursday 14 February 2013 11:54:38 John Murphy did
opine:
Thanks for that Gene. Really interesting. I tried searching the net
for anything which would provide more information, and about all I could
quickly find was where older Linux kernels used 'edge detection' for
interrupts as opposed to 'level detection'. I see LinuxCNC still uses
either 2.4 or 2.6 kernels, which are the ones mentioned in the article.
Maybe things have improved with all the fine work which has gone into
the kernel since then. In Linus I trust. ;)
On Wed, 13 Feb 2013 21:12:57 -0800, Len Ovens
wrote:
John, in my experience, you are shooting yourself about kneecap high by
running the nvidia driver. It gets part of its performance by locking out
the interrupts, for extended periods of time. For an app that needs true
real time, such as linuxcnc, a 5 microsecond base thread jitter in its
timing, has been logged as creating latency jitters in the 200 millisecond
range. Even for the more forgiving servomotor stuff its not good, and its
totally intolerable for steppers which need a steady heartbeat to move at
more than creep speeds. On Wed, February 13, 2013 8:59 pm, John Murphy
wrote:
It certainly makes for a very slick distro and one I'll probably use
until KDE5, if not forever!
Tried one more time with the low-latency 3.8.0.6 kernel, but no go.
As soon as I rebooted after installing Generic, nvidia-310-dev was
up and running, which is great. Means I'll be able to compare the
performance of the two kernel types, which could be useful.
Thanks. Well I just tried an Xubuntu 13.04
'daily' build and, similarly to
Ubuntu, I got a login prompt without X running and installed
nvidia-310-dev, which works OK. It takes ages, compared to Studio,
to boot from Grub to login though, so there's some magic under the
hood of the Studio version I think.
Ubuntustudio took xubuntu as it's start at 11.10 and probably hasn't
merged in any new stuff xubuntu has since then. So there may just be
less stuff in Studio. The nouveau driver gained some support for the 3d
stuff recently, and it
should be checked out to see if it makes the xruns and such worse or
better. As a final check to see if the video is an xrun causer, try the
vesa driver, there have been times when I was forced to use it on my
machine tool (cnc machinery) controllers. Poor display of course, but the
machine worked great.
It will be easy enough to compare as the low-latency kernel can't
work as is with the Nvidia driver, so I'll be able to switch between
Generic + Nvidia and low-latency + Nouveau. I may have already used
the Vesa driver. I was limited to 640x480 at one stage. :)
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