On Fri, 2009-07-03 at 11:54 +0000, jbl wrote: > [11:52:41] <jbl:#linux-rt> +jonmasters: ping > [11:53:27] <jbl> +how long should be max latencies seen with hwlat detector? It's a US holiday, so I'll reply by email as I'm not really around for IRC, but I don't want to forget to add something to this - especially as people seem to be trying to also track down new latencies in RT itself. I don't think these are SMI related - though now you can check. The default for the latency detector is to regard any unexplained time interval over (greater than, not greater than or equal to) 10us as a latency worthy of some regard. But you can also configure it down to 1us since anything over 0us represents some kind of interruption - it's all down to what threshold you actually care about (few people notice 1us). Anyway. How high should it go? Theoretically, that is an open ended question. But we have seen in practice latencies up to many milliseconds or even higher - I don't expect you'll go over 100ms and in reality, I don't expect it to be anything like that, maybe hundreds of us on a modern enough system. But the range is really down to whatever crap the BIOS is doing when it's taking your CPU cycles away, and that could literally be anything (reformulating the coke recipe isn't unlikely). If you're seeing something irregular, for widely long periods of time it is less likely to be the kind of SMIs we see, which do tend to be semi-predictable as they rely upon counters for most of the non-asynchronous (e.g. hardware emulation) activities. But if you see something short many times per second, or something longer on a predictable schedule then it is quite likely to be an SMI hitting you. Jon. P.S. I know there's a slight bug in the wake_up handling in hwlat that is causing some issues - I will have a fix available next week. -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
