linear aggregation

[brendangregg]

Something that seems missing is an easy way to bucketize data, such as a linear aggregation. For example, I want to store latency in 10 ms buckets, from 0 to whatever the maximum observed latency is, and print it out as a histogram.

Here's an example workaround using the current capabilities. First, the example output:

# ./sysagg.kp 
Tracing syscalls... Hit Ctrl-C to end.
^C
   LAT(ms)+    COUNT
          0      378
         10        0
         20        0
         30        1
         40        0
         50        0
         60        0
         70        2
         80        0
         90        0
        100       33
        110        0
        120        2
        130        0
        140        2
        150        0
        160        2

This would be even better as a histogram.

And the script:

#!/usr/bin/env ktap
#
# sysagg.kp syscall latency linear aggregation
#
#10-Nov-2013   Brendan Gregg   Created this

step = 10   # number of ms per step

self = {}
lats = {}
max = 0

print("Tracing syscalls... Hit Ctrl-C to end.")

trace syscalls:sys_enter_* {
    self[tid()] = gettimeofday_us()
}

trace syscalls:sys_exit_* {
    if (self[tid()] == nil) { return }
    delta = (gettimeofday_us() - self[tid()]) / (step * 1000)
    if (delta > max) { max = delta }
    lats[delta] += 1
    self[tid()] = nil
}

trace_end {
    printf("   %8s %8s\n", "LAT(ms)+", "COUNT");
    for (i = 0, max, 1) {
        printf("   %8d %8d\n", i * step, lats[i]);
    }
}

[ktap]

Hi Brendan,

You are right, there also lack data bucketize functionality in ktap,
I will take look at deeply to find out a proper design for ktap.

Hopefully this line aggregation and key sorting functionality will
be support in next release(v0.4).

And again, do you willing to let this script to be a sample script
in ktap tree?

Thank you very much.

Jovi

[brendangregg]

Thanks, data bucketize will be useful. Yes, you are welcome to include it in the ktap tree; it's from a simple page I created of ktap examples (http://www.brendangregg.com/ktap.html). Not much there yet, but as I use ktap more I will probably come up with more things that might be useful to include.

[ktap]

Thank you very much, that page would be a good tutorial for ktap. :)

(I will keep this issue open until ktap support linear aggregation, and other two issues.)