(2014/02/09 23:37), Ingo Molnar wrote: > > * Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx> wrote: > >> I guess the second reason is why the stap takes so long time to set >> probes. stap tries to register kprobes without disabled flag, that >> means we enables thousands of probes (overheads). >> >> So the similar thing happens when we enables events as below; >> >> # for i in /sys/kernel/debug/tracing/events/kprobes/* ; do date; echo 1 > $i; done >> Wed Jan 29 10:44:50 UTC 2014 >> ... >> >> I tried it and canceled after 4 min passed. It enabled about 17k >> events and slowed down my system very much(I almost got hang check >> timer). > > Ok, I guess that's the slowdown bug that Frank reported. > >> I think we should have some performance statistics (hit count?) and >> if it goes over a threshold, we should stop enabling other events. > > That really feels like a hack. How about fixing the root cause? Does > the enabling of all probes have to be so slow? When I tried to use perf top, most of the time was consumed in kprobe_ftrace_handler and optimized_callback, both of them are the handler of kprobes. Since I just tried on a VM guest and it didn't support NMI nor PMU, thus I have to use a bare metal machine for deeper investigation (and I'll do). And yes, it seems that the performance problem comes from probing and tracing itself. Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@xxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
