On Mon, Nov 18, 2013 at 09:59:45AM -0300, Arnaldo Carvalho de Melo wrote: > Em Fri, Nov 15, 2013 at 06:46:09AM +0100, Ingo Molnar escreveu: > > btw., here's some 'perf top' call graph performance and profiling > > quality feedback, with the latest perf code: > > > > 'perf top --call-graph fp' now works very well, using just 0.2% > > of CPU time on a fast system: > > > > 4676 mingo 20 0 612m 56m 9948 S 1 0.2 0:00.68 perf > > > > > > > > 'perf top --call-graph dwarf' on the other hand is horrendously > > slow, using 20% of CPU time on a 4 GHz CPU: > > > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > > > > > > 4646 mingo 20 0 658m 81m 12m R 19 0.3 0:18.17 perf > > > > On another system with a 2.4GHz CPU it's taking up 100% of CPU > > time (!): > > > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > > > > > > 8018 mingo 20 0 290320 45220 8520 R 99.5 0.3 0:58.81 perf > > > > > > Profiling 'perf top' shows all sorts of very high dwarf > > processing overhead: > > Yeah, top dwarf callchain has been so far a proof of concept, it > exacerbates problems that can be seen on 'report', but since its live, > we can see it more clearly. > > The work on improving callchain processing, (rb_tree'ing, new comm > infrastructure) alleviated the problem a bit. > > Tuning the stack size requested from the kernel and using --max-stack > can help when it is really needed, but yes, work on it is *badly* needed.
agreed ;-) also there's new remote unwind interface recently added into libdw, which seems to be faster than libunwind. I plan on adding this soon. jirka -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
