On 03.10.19 17:23, Rossier Daniel via Xenomai wrote:
Hi all,
We are currently working on a project called OpenCN which is a framework deeply
inspired from LinuxCNC, but with a revisited architecture.
Hence, OpenCN is related to machine control.
Our framework mainly use a AMP approach and runs the Xenomai/Cobalt kernel on a
dedicated CPU with no I-pipe (reworked out).
(We plan to release the framework by first of November).
IOW, "bare-metal" Cobalt? Collaborative AMP, or partitioned via virtualization?
Our framework works well on a x86 PC, but we have to face an issue regarding
DMA priority between the GPU and CPU; when the user plays with the GUI,
some small latencies (O(10ms)) raise up.
Although the question is not directly related to Xenomai, I would be very
interested if somebody knows if it possible to give CPU priority against the
GPU,
and how to manage the related DMA controller? Is it possible to configure it ?
Or any other hint to avoid this latency ?
Many thanks in advance for any inputs.
I didn't dig into anything that manages PCI bandwidth yet. I heard that
something exists, but at that time it was not publicly documented. And it's
likely highly platform specific (SoC/chipset).
Did you clearly identify that it's DMA contention which increased your latency?
Do you cache-miss delays increase (PMU should tell you)? Or is there a
contention between a RT device doing DMA and the GPU?
Jan
--
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux
