> > Have you tried to use 'perf probe' to achieve any useful > instrumentation on a real app? > > I just tried out the 'glibc:free' usecase and it's barely > usable. > Thanks for trying. Yes, I have actually place probes on free and malloc while building a kernel and it has worked for me. > Firstly, the recording very frequently produces overruns: > > $ perf record -e probe_libc:free -aR sleep 1 > [ perf record: Woken up 169 times to write data ] > [ perf record: Captured and wrote 89.674 MB perf.data (~3917919 samples) ] > Warning:Processed 1349133 events and lost 1 chunks! > I have seen the "lost chunks" but thats not always and mostly when I have run perf record for a very long time. But I have seen this even with just kernel probes too. So I didnt debug that. > Using -m 4096 made it work better. > > Adding -g for call-graph profiling caused 'perf report' to lock > up: > > perf record -m 4096 -e probe_libc:free -agR sleep 1 > perf report > [ loops forever ] > This actually works for me. I had CONFIG_PREEMPT not set. So I set it and tried with and without Jiri's fix. It still worked for me. Can you pass me your config that shows this hang so that I can try and fix it. > I've sent a testcase to Arnaldo separately. Note that perf > report --stdio appears to work. There are no changes in perf report because of uprobes. So the data collected from uprobes could trigger the hang. I was speculating that not disabling preemption that Jiri pointed out could be causing this. So I tried with and without but couldnt reproduce. Can I request you to see if Jiri's patch helps? Today with -g option, on one machine I do see a $ sudo perf report perf: Floating point exception I will take a look at this too. Other machines dont seem to show this error. > Regular '-e cycles -g' works fine, so this is a uprobes specific > bug. > -- Thanks and Regards Srikar -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>