#!/usr/bin/env bpftrace

/* Script to obtain ksys_write() latency histograms.
 * It will measure time between entry and exit and plot one histogram
 * for each destination port number, indicating the amount of time spent.
 *
 * Implemented 2026 by Pau Espin Pedrol <pespin@sysmocom.de>
 * SPDX-License-Identifier: CC0
 *
 * As no filtering on PID etc. is done, you will likely use this with 'bpftrace -p' like
 *
 *     bpftrace ./ksys_write.bt -p PID
 *
 * (where PID is the PID of the process, like osmo-bts-trx)
 */

BEGIN
{
  printf("Tracing ksys_write() latency... Hit Ctrl-C to end.\n");
}

kprobe:ksys_write
{
  $fd = (int64)arg0;

  @start[tid] = nsecs;
  @fd[tid] = $fd;
}

kretprobe:ksys_write / @start[tid] /
{
  $delta_us = (nsecs - @start[tid]) / 1000;
  @latency[@fd[tid]] = hist($delta_us);

  delete(@start[tid]);
  delete(@fd[tid]);
}

/* vim:set ts=2 sw=2 et: */