Em Thu, Sep 18, 2014 at 04:17:13PM -0300, Arnaldo Carvalho de Melo escreveu: > Em Thu, Sep 18, 2014 at 06:37:47PM +0200, Milian Wolff escreveu: > > This was also why I asked my initial question, which I want to repeat once > > more: Is there a technical reason to not offer a "timer" software event to > > perf? I'm a complete layman when it comes to Kernel internals, but from a > > user > > point of view this would be awesome: > > > perf record --call-graph dwarf -e sw-timer -F 100 someapplication > > > This command would then create a timer in the kernel with a 100Hz > > frequency. > > Whenever it fires, the callgraphs of all threads in $someapplication are > > sampled and written to perf.data. Is this technically not feasible? Or is > > it > > simply not implemented?
What you want is a sysrq-t that goes all the way to userspace, right? Try: echo t > /proc/sysrq dmesg i.e. probably you want that when a thread goes to sleep, we can take a sample with callchains, no? With a 'ping 127.0.0.1' running, I get this for its process: [19255.244315] ping S ffff88043e213100 0 6754 6548 0x00000080 [19255.244316] ffff880231693a80 0000000000000082 ffff88040ffb1940 0000000000013100 [19255.244317] ffff880231693fd8 0000000000013100 ffff880423c88000 ffff88040ffb1940 [19255.244318] ffffffff81efb1c0 ffff880231693ab0 00000001012131d1 ffffffff81efb1c0 [19255.244319] Call Trace: [19255.244321] [<ffffffff816b93a9>] schedule+0x29/0x70 [19255.244322] [<ffffffff816bbf91>] schedule_timeout+0x151/0x270 [19255.244325] [<ffffffff815ac606>] __skb_recv_datagram+0x426/0x4d0 [19255.244328] [<ffffffff815ac6e2>] skb_recv_datagram+0x32/0x40 [19255.244330] [<ffffffff8161a1ad>] raw_recvmsg+0x7d/0x1b0 [19255.244331] [<ffffffff8162961c>] inet_recvmsg+0x6c/0x80 [19255.244333] [<ffffffff8159d42a>] sock_recvmsg+0x9a/0xd0 [19255.244345] [<ffffffff8159e1a2>] __sys_recvmsg+0x42/0x80 [19255.244346] [<ffffffff8159e1f2>] SyS_recvmsg+0x12/0x20 [19255.244348] [<ffffffff816bd412>] system_call_fastpath+0x16/0x1b No? Trying to collect dwarf callchains after installing iputils-debuginfo (where /bin/ping symtab is)... > > I'm experimenting with a libunwind based profiler, and with some ugly > > signal > > hackery I can now grab backtraces by sending my application SIGUSR1. Based > > on > > Humm, can't you do the same thing with perf? I.e. you send SIGUSR1 to > your app with the frequency you want, and then hook a 'perf probe' into > your signal... /me tries some stuff, will get back with results... > > > that, I can probably create a profiling tool that fits my needs. I just > > wonder > > why one cannot do the same with perf. > > - Arnaldo -- To unsubscribe from this list: send the line "unsubscribe linux-perf-users" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
