How to inject sleep

[Bryn M. Reeves]

On Wed, Apr 18, 2018 at 12:16:17PM +0530, Nayan Gadre wrote:
> probe module("llt").function("llt_send_data"){
>          print("LLT_SEND_DATA\n");
>          printf("Arguments: [Port: %u, Nid: %u, FragCount: %u,
> Frag_size: %u]\n", $port, $nid, $fcnt, $frags[0]->f_size);
>          #printf("local variables %s and arguments %s\n", $$locals, $$vars)
>          print_backtrace()
>          print("-------------------------------\n")
>  }
> 
> So would like to inject msleep(10) after entering into this module
> function llt_send_data.

You can't sleep (since that would involve scheduling), but you can
brief busy-waits using the guru-delay tapset.

I wrote this a few years back to allow injecting short pauses into
driver code for fault simulation, and it's proven useful for a few
other situations since.

You should find it in /usr/share/systemtap/tapset/dyninst/guru-delay.stp
or so, and the functions provided are:

  mdelay(ms)
  udelay(us)

It does require guru-mode (-g) to use, since it can induce quite
dramatic system-wide side effects if used incautiosly.

Regards,
Bryn.