Jan Kiszka wrote:
John Schipper wrote:
Hello,
I'm new to this list but have in the past used RTAI in a single
processor off the shelf solution. I'm looking to switch to native
Xenomai api but have a general problem...
The problem is SMI on new systems, and other latency killers that
What do you mean with "other" precisely?
I have seen on systems the need to disable USB Legacy/emulation? and
only use a PS/2 keyboard. The USB interface (tied to a usb keyboard and
mouse) are standard on a Dell GX280 without a PS/2 interface. I believe
and have seen real-time having problems. This is due to to SMM mode, I
believe, being a latency killer (not sure if this is SMI related).
In regard to SMI I poked around the intel chips registers (sorry can't
remember what the GX280 chipset was but I could get it if important! )
and I found that their are lock bits that do not allow disabling global
SMI or the watchdog capability. This was 6 months ago at least so I
have not tested the latest smi workaround module (in RTAI at least
because I have not use xenomai yet but plan too :) )
sometimes are not controllable by software always popping up when trying
to migrate to a newer platform. Can a dual core processor using
isolcpus, preemp-rt and xenomai effectively future proof agains smi/chip
set issues (specificly AMD or Intel dual core solutions) by isolating a
cpu for exclusively xenomai/realtime use?
SMI can only be addressed with CPU isolation if you are able to redirect
the related event only to one CPU. Don't know if this is possible /
default.
This redirection has occured to me also. A couple months ago I
inquired and did not get any confirmation either way from Dell about
doing this and maybe they do not know and I need to ask
Intel/Via/AMD?...... Its not clear (if even possible ) to me if this
would be a bios feature or only controlled by using a special chipset
kernel patch or module?
There are tricks to disable SMI on modern Intel chipsets. Xenomai
implements this, you can select the workaround during system
configuration. Don't this work for your particular systems? Then please
report details.
SMI tricks had not worked on a Dell GX280 system but I plan to start
some more testing again with xenomai. The fact that it did not work
prompted me to dig into the SMI/SMM registers and is where I discovered
that I could not get past the lock bit capability of the SMI/SMM chipset
that was being set by the bios (not positive this is where it was
happening ) and after some failed attempts I just continued with the
Dell 170/270 solution. If there is an advantage or maybe even a hope :)
that an isolated cpu will help in regards to SMI/SMM then I plan to go
ahead and order some systems to test otherwise I may continue to try to
testing single core solutions.
"Other", more subtle latency issues can only be addressed when the
mechanisms behind them are understood. Depends on the chipset
manufacturer's documentation. So, no general answer is possible.
Some background information: The realtime software I've developed in
the past (with RTAI/adeos in user space) is a simple high speed
serializer driver (mmap) to communicate with outside hardware and is
responsible for syncronizing (with a semaphore/mutex) a linux process
(soft realtime) at ~60Hz. The realtime process is periodic at 1.2Khz or
2.4Khz and calculates/filters the data before sending commands back down
the serializer interface and to the linux process for soft realtime
network access.
Generally we like to use "off the shelf" business PC's (Dell 170's and
Dell 270's, HP 5000 with 1Gig memory) and find that 20-30us latency is
achievable. We use "off the shelf" hardware because availability
(recieve within a week) and low cost are desired. Whenever looking for
an alernative solution either availablity or cost becomes a show
stopper. I'm open to suggestions and invite anyones thoughts on the
subject.
Using off the shelf standard systems is always risky. I've heard of a
larger German automation company ordering standard PC hardware for
industrial control purposes only when initial latency tests on a
specific charge were successful. Ok, they are ordering large enough
quantities, so they can dictate certain conditions...
Testing the system is done to verify latency and expected real-time
isolation from the normal linux tasks. Its done on a standard system and
once verified used until the system is no longer available which seems
to be happening at an increasing rate. PCI express may be a reason,
maybe money.. but systems don't last much longer then a year and a
half. Either way the motherboards themselves don't stay around to
long. Our quantity is not there for the needed leverage with providers
:( . The system is used for an industrial purpose which is NOT for a
life saving/risking situation. Its used for simulation or simulator
purposes.
Jan
John
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