Hi Tom
Thanks for your thorough reply. I am not
in front of the workstation but I’ll use the gpu
activity monitor to guess if chimera is using the
three GPUs. I have some doubts that the OS / openGL
driver is distributing rendering work on each gpu in
our configuration. I think that for the SLI to work
you need to wire both cards together, which is not
the case in our workstation. But anyway, I’ll check
activity.
The rendering case I was referring to
consists of solid rendering. I never try to render
the full dataset at full resolution as we are
talking about datasets of around 50 Gb. I use a very
high step to select a sub region, then I gradually
decrease step size and fine tune the contrast
transfer function. When I am happy I render at step
2 or step 1, depending on the sub region size.
Clearly there is time needed to read data from disk;
when reading is done the program still computes
stuff for a few seconds. Then I can rotate, zoom, …,
the volume. If the sub region is not too large then
it is super smooth. But if I select a too large sub
volume, then I can rotate some degrees, then it
freezes for a while, then it is smooth again, etc.
So I guess it corresponds to your description of the
problem.
I took a look at the benchmark. That’s
very useful! Obviously I am not going to get better
performance with a quadro (at least one in the
benchmark: All quadro except K4000 get worse scores
for solid rendering than the GTX 780 Ti. K4000
actually got the same score as the 780 Ti. Only with
a GTX Titan would I get a nearly 2x improvement,
which makes sense since this card has 2x the memory
of the 780 Ti (6Gb vs 3Gb). The GTX Titan X is not
in the benchmark yet but it should be even better as
it has 12 Gb Ram. Possibly the quadro k6000, which
is not in the benchmark either, could have similar
or better performance as this one (it also has 12 Gb
RAM) but … it costs about 4 times more than a Titan
X. Sad that only the quadro work for stereo under
linux (but for that we bought a once state of the
art quadro on eBay for 150$ and installed it on
another PC :-)
Cheers
Ben
Hi Ben,
I haven’t tried Chimera with 2
or more graphics cards working together. I
don’t know if it is likely to improve
rendering speed. I don’t think applications
need any special support to use multiple cards
— the system graphics driver distributes the
work across 2 or more cards. With Nvidia
cards this technology is called SLI and with
AMD cards it is called CrossFire. From what I
understand they do thing like have each of 2
cards render every other frame — since the
graphics are pipelined the current frame and
next frame could be rendered simultaneously
possibly doubling the speed. I have my doubts
that this will improve Chimera rendering speed
for large density maps. I think slow
rendering of maps in solid (grayscale) style
typically happens in Chimera when the map data
doesn’t fit on the graphics card, so every
frame it has to transfer all the data to the
card — the performance plummets once you get a
map that big. If the data does fit on the
graphics card, it usually renders at full
frame rate (60 frames per second), although
that isn’t true of all graphics cards. This
all relates to the speed rotating the model.
When you first load a big map it can take a
long time because disk drive speed is slow — a
solid state drive helps speed this up. If you
explain exactly the case where you see slow
rendering I can perhaps advise.
In general I think the Geforce
cards perform better (fewer bugs, faster
speed) than the Quadro cards, and would only
recommend Quadro if you use stereoscopic
display with shutter glasses. Here are
Chimera benchmarks for a range of graphics
cards:
Tom
On Dec 17, 2015, at 5:28 AM,
wrote:
Hi
Can chimera make use of
more than one GPU for 3D rendering?
We have 3 Geforce GTX 780 Ti (mainly
used for number crunching) on a
particular workstation and would be
interested to make full use of them
for rendering tomograms or serial
block face imaging data.
Another question: has
anyone done benchmark comparison for
3D rendering in Chimera between a
top of the line Geforce GTX card and
a top Quadro card? Is there a strong
improvement with the Quadro, which
might justify the price gap?
Thanks
Ben
Institute of Anatomy
University of Bern
Baltzerstrasse 2
Postfach 922
3000 Bern 9
Switzerland
+41 31 631 84 40
_______________________________________________
Chimera-users mailing list
Chimera-users@cgl.ucsf.edu
http://plato.cgl.ucsf.edu/mailman/listinfo/chimera-users