Messages in this thread | | | Date | Thu, 18 May 2006 10:56:40 +0200 | From | Ingo Molnar <> | Subject | Re: rt20 scheduling latency testcase and failure data |
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* 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.
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