On Thu, Aug 14, 2014 at 3:13 PM, Brendan Gregg <brendan.d.gr...@gmail.com> wrote: > On Wed, Aug 13, 2014 at 12:57 AM, Alexei Starovoitov <a...@plumgrid.com> > wrote: >> this example has two probes in C that use two different maps. >> >> 1st probe is the similar to dropmon.c. It attaches to kfree_skb tracepoint >> and >> count number of packet drops at different locations >> >> 2nd probe attaches to kprobe/sys_write and computes a histogram of different >> write sizes >> >> Usage: >> $ sudo ex2 >> >> Should see: >> writing bpf-5 -> /sys/kernel/debug/tracing/events/skb/kfree_skb/filter >> writing bpf-8 -> /sys/kernel/debug/tracing/events/kprobes/sys_write/filter >> location 0xffffffff816efc67 count 1 >> >> location 0xffffffff815d8030 count 1 >> location 0xffffffff816efc67 count 3 >> >> location 0xffffffff815d8030 count 4 >> location 0xffffffff816efc67 count 9 >> >> syscall write() stats >> byte_size : count distribution >> 1 -> 1 : 3141 |**** | >> 2 -> 3 : 2 | | >> 4 -> 7 : 14 | | >> 8 -> 15 : 3268 |***** | >> 16 -> 31 : 732 | | >> 32 -> 63 : 20042 |************************************* | >> 64 -> 127 : 12154 |********************** | >> 128 -> 255 : 2215 |*** | >> 256 -> 511 : 9 | | >> 512 -> 1023 : 0 | | >> 1024 -> 2047 : 1 | | > > This is pretty awesome. > > Given that this is tracing two tracepoints at once, I'd like to see a > similar example where time is stored on the first tracepoint, > retrieved on the second for a delta calculation, then presented with a > similar histogram as seen above.
Very good point. The time related helpers are missing. In V5 I'm thinking to add something like bpf_ktime_get_ns(). To associate begin and end events I think bpf_gettid() would be needed, but that doesn't feel generic enough for helper function, so I'm leaning toward 'bpf_get_current()' helper that will return 'current' task pointer. eBPF program can use this pointer for correlation of events or can go exploring task fields with bpf_fetch_() helpers... Thank you very much for trying things out and for your feedback! -- 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/
