Messages in this thread | | | Subject | Re: rt20 scheduling latency testcase and failure data | From | Sébastien Dugué <> | Date | Thu, 18 May 2006 11:18:09 +0200 |
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On Thu, 2006-05-18 at 10:56 +0200, Ingo Molnar wrote: > * Sébastien Dugué <sebastien.dugue@bull.net> wrote: > > > > thanks for tracking this down. FYI, the latency of stopping the trace is > > > that expensive because we are copying large amounts of trace data > > > around, to ensure that /proc/latency_trace is always consistent and is > > > updated atomically, and to make sure that we can update the trace from > > > interrupt contexts too - without /proc/latency_trace accesses blocking > > > them. The latency of stopping the trace is hidden from the tracer itself > > > - but it cannot prevent indirect effects such as your app from missing > > > periods, if the periods are in the 5msec range. > > > > > > > Thanks for the explanation, will have to look deeper into the code > > to understand how it works though. > > there's another complexity on SMP: if trace_all_cpus is set then the > per-cpu trace buffers are sorted chronologically as well while the > copying into the current-max-trace-buffer, to produce easier to read > latency_trace output. > Well, that's not the case here, but thanks for the info.
Sébastien.
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