I wrote the cgroups stuff, but in fact have very little experience on different
systems (and understand very little the ins-and-outs of shared cache, memory
banks, NUMA architecture, etc.). I can say that on the J1900, though, where
two L2 caches are each shared by two of the CPU's four cores, allowing OS
processes to run on a core sharing cache with the core running the RT threads
killed our excellent results, and jitter measurements returned to those for
conventional configurations without CPU isolation.
Your guess about memory infighting seems to make sense in our tests, but if
it's not too difficult, maybe it's still worth a try since your system isn't
exactly the same? Also, I don't understand your comment about the DDR4 memory;
is that a second stick you'd add to the J5005? (Our J1900s have only one
SODIMM.) In any case, I'd appreciate hearing about any results on any CPU.
OT, we encountered one interesting result entirely by accident: With CPU
isolation on the same J1900, a misconfiguration caused POSIX thread selection
instead of the intended RT_PREEMPT; however we didn't notice because we still
saw the same excellent sub-7uS jitter!
John
________________________________________
From: [email protected] <[email protected]> on behalf of
[email protected] <[email protected]>
Sent: Wednesday, March 6, 2019 9:28 PM
To: Machinekit
Subject: Re: [Machinekit] cgroups and isolating CPU’s
Yes, thank you. I have been reading this document since before it was merged.
I know that usability for me is currently zero, but I am interested in
technology and development. I have one unused DDR4 stick from notebook upgrade,
but the J5005 seems like no good choice as by datasheet the L2 cache is shared
across all cores. (So I guess memory infighting would occur.)
C.
Dne středa 6. března 2019 13:04:06 UTC+1 John Morris napsal(a):
Bas is right. Here's the referenced documentation in context.
http://<http://www.machinekit.io/docs/hal/threads-and-latency/>www.machinekit.io<http://www.machinekit.io/docs/hal/threads-and-latency/>/docs/<http://www.machinekit.io/docs/hal/threads-and-latency/>hal<http://www.machinekit.io/docs/hal/threads-and-latency/>/<http://www.machinekit.io/docs/hal/threads-and-latency/>threads-<http://www.machinekit.io/docs/hal/threads-and-latency/>and-latency<http://www.machinekit.io/docs/hal/threads-and-latency/>/<http://www.machinekit.io/docs/hal/threads-and-latency/>
If you have no CPUs to spare, though, this will be of no use to you.
John Morris
Dovetail Automata LLC
From: Bas de Bruijn
Sent: Thursday, February 28, 13:43
Subject: [Machinekit] cgroups and isolating CPU’s
To: [email protected]
Cc: Machinekit
So as not to hijack the thread, a new thread
On 28 Feb 2019, at 19:20, [email protected] wrote:
BTW, did someone else (than Zultron) try to use the core isolation feature to
"turn on" back the step signal generation in software? My electrotrash which I
use for Machinekitdoes not have cores to spare.
Yes, you’re probably referring to this?
https<https://github.com/machinekit/machinekit/pull/1426>://<https://github.com/machinekit/machinekit/pull/1426>github.com<https://github.com/machinekit/machinekit/pull/1426>/<https://github.com/machinekit/machinekit/pull/1426>machinekit<https://github.com/machinekit/machinekit/pull/1426>/<https://github.com/machinekit/machinekit/pull/1426>machinekit<https://github.com/machinekit/machinekit/pull/1426>/pull/1426<https://github.com/machinekit/machinekit/pull/1426>
Although i dont use software step generation. The latency obtained is very good
(6-7 us).
What was done here is to force the thread to run on designated cpu’s.
Because these cpu’s were isolated during startup (isolcpus= kernel parameter)
there are no other processes running on these cpu’s.
These cpu’s must be the pair that share their L2 cache, or hyperthreading
should be disabled and that cpu used.
A setup that was historically used with iolcpus= kernel parameters was to run
everything on 1 cpu (disabling all but one), so that the cpu was hogged and
that got good latency results.
This cgroups setup is the other way around, you’ll only run HAL on the isolated
cpu’s, the /RT cpuset.
I’m no expert on this so there might be some more clarification needed from the
experts :)
Bas
--
website:
http://<http://www.machinekit.io>www.machinekit.io<http://www.machinekit.io>
blog:
http://<http://blog.machinekit.io>blog.machinekit.io<http://blog.machinekit.io>
github:
https<https://github.com/machinekit>://<https://github.com/machinekit>github.com<https://github.com/machinekit>/<https://github.com/machinekit>machinekit<https://github.com/machinekit>
---
You received this message because you are subscribed to the Google Groups
"Machinekit" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
Visit this group at
https<https://groups.google.com/group/machinekit>://<https://groups.google.com/group/machinekit>groups.google.com<https://groups.google.com/group/machinekit>/group/<https://groups.google.com/group/machinekit>machinekit<https://groups.google.com/group/machinekit>.
For more options, visit
https<https://groups.google.com/d/optout>://<https://groups.google.com/d/optout>groups.google.com<https://groups.google.com/d/optout>/d/<https://groups.google.com/d/optout>optout<https://groups.google.com/d/optout>.
--
website: http://www.machinekit.io blog: http://blog.machinekit.io github:
https://github.com/machinekit
---
You received this message because you are subscribed to the Google Groups
"Machinekit" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to
[email protected]<mailto:[email protected]>.
Visit this group at https://groups.google.com/group/machinekit.
For more options, visit https://groups.google.com/d/optout.
--
website: http://www.machinekit.io blog: http://blog.machinekit.io github:
https://github.com/machinekit
---
You received this message because you are subscribed to the Google Groups
"Machinekit" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
Visit this group at https://groups.google.com/group/machinekit.
For more options, visit https://groups.google.com/d/optout.
