Messages in this thread | | | Date | Sat, 16 Sep 2006 21:10:43 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108 |
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* Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote:
> See http://ltt.polymtl.ca/svn/tests/kernel/test-kprobes.c to insert > the kprobe. Tests done on LTTng 0.5.111, on a x86 3GHz with > hyperthreading.
i have done a bit of kprobes and djprobes testing on a 2160 MHz Athlon64 CPU, UP. I have tested 2 types of almost-NOP tracepoints (on 2.6.17), where the probe function only increases a counter:
static int counter;
static void probe_func(struct djprobe *djp, struct pt_regs *regs) { counter++; }
and have measured the overhead of an unmodified, kprobes-probed and djprobes-probed sys_getpid() system-call:
sys_getpid() unmodified latency: 317 cycles [ 0.146 usecs ] sys_getpid() kprobes latency: 815 cycles [ 0.377 usecs ] sys_getpid() djprobes latency: 380 cycles [ 0.176 usecs ]
i.e. the kprobes overhead is +498 cycles (+0.231 usecs), the djprobes overhead is +63 cycles (+0.029 usecs).
what do these numbers tell us? Firstly, on this CPU the kprobes overhead is not 1000-2000 cycles but 500 cycles. Secondly, if that's not fast enough, the "next-gen kprobes" code, djprobes have a really small overhead of 63 cycles.
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