Messages in this thread | | | Subject | Re: preempt-rt, NUMA and strange latency traces | From | john stultz <> | Date | Thu, 09 Feb 2006 10:54:21 -0800 |
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On Thu, 2006-02-09 at 12:11 +0100, Sébastien Dugué wrote: > On Wed, 2006-02-08 at 08:49 -0800, john stultz wrote: > > On Wed, 2006-02-08 at 11:45 +0100, Sébastien Dugué wrote: > > > The more I think about it, the more I tend to believe it's hardware > > > related. It seems as if the CPU just hangs for ~27 ms before > > > resuming processing. > > > > That sounds like to the ~30ms RSA caused SMIs. Does this system have an > > RSA1 or RSA2 card? > > > > 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.
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.
> 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.
thanks -john
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