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SubjectRe: [PATCH RFC v4 net-next 25/26] samples: bpf: counting eBPF example in C
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On Wed, Aug 13, 2014 at 12:57 AM, Alexei Starovoitov <ast@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.

Brendan


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