Messages in this thread | | | Subject | Re: preempt-rt, NUMA and strange latency traces | From | Sébastien Dugué <> | Date | Fri, 10 Feb 2006 14:07:45 +0100 |
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On Thu, 2006-02-09 at 10:54 -0800, john stultz wrote: > > > > I think it's an RSA1 card, but no certainty here. I don't think > > the x440 came with the RSA2. Is there a way to check for sure without > > unplugging everything (It's such a mess of cables behind the box)? > > No, you're right, the x445 was the box that could have either RSA1 or > RSA2. The x440 can only have an RSA1. > > > > Whats the SMI issue with the RSA? Could the RSA generate bursts of SMI > > that could be enough to freeze the CPUs? > > SMIs effectively freeze all cpus while the BIOS code executes. With the > RSA1, there are two main causes of SMIs: > 1) Periodic SMI: Which occurs every 15 minutes as the RSA checks various > hardware status and lasts for ~30ms. > > 2) Console Redirection SMIs: This occurs only when you use the console > redirection feature from the RSA. You'll see ~30ms stalls ~once a second > while the SMI screen-scrapes the console text buffer and sends it out > over the serial line.
That must be what I've been hitting in my tests and will check soon.
> > The console redirection one is easy to avoid: just don't use that > feature if you care about low latencies. The periodic SMI is more > difficult to work around. With RSA2 based systems, there is a BIOS > update that allows you to disable this functionality (and on newer > systems it ships disabled), however I don't believe there is any such > feature for the older RSA1 based systems.
I'll have to live with it then.
> > > > When I ran those tests I was logged on the RSA (serial line). I will > > try to run the tests again without being connected when I can manage to > > get some CPU time (eh! shared machine)... > > Yes, not using the console redirection feature will definitly help the > situation, but there still will be the possibility of ~30ms stalls every > 15 minutes on the x440.
That's the problem and I'll have to synchronize for a proper window for running my tests.
Is this SMI thing IBM's eyes only stuff or is it documented somewhere?
Thanks for that valuable info.
Sébastien.
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