minutes: IO Visor TSC and Dev Members Call

Brenden Blanco <bblanco@...>

Hi all,

Thanks for joining the call today. Below is the summary of the topics

If you are in the Bay Area tomorrow, PLUMgrid will be hosting a meetup
to discuss XDP, feel free to join if you can.


On the kernel side, two patches landed recently, both should be
available in Linux 4.8:

From myself, the initial xdp framework was accepted into net-next.

From Sargun Dhillon, experimental support for writing into process memory
from a kprobe.

Brendan has been working on some excellent documentation, adding:
  - An end user guide
  - A developer tutorial
  - A developer reference guide

Alban had 2 questions/use cases that he shared:
1. Monitor all local connections on a machine
  Current approach does effectively:
  - get a list of sockets
  - usually look in /proc/$PID/...
    - racy
    - not for short-lived connections
    - poll-heavy
  Instead would like to:
  - trace connect()/accept()/send()...
    - kprobe can fill the gap for now
    - still need tracepoints for tcp+sockets, reliable api
    - would be nice to have multiple bpf programs per kprobe
      - this has been brought up before, possible to use tail calls to
        implement this in bcc without new kernel features
2. Monitor all services in a cgroup, e.g. network bytes sent/recd
  - Kprobes are global, but often have access to cgroup pathname
  - Possible to filter/bucket kprobe statistics based on this, but
    relies on kernel data structures...fragile
  - Suggest to formalize use case to iovisor-dev list, possible new bpf
    program type/helper to be discussed there

Brendan mentioned a new observability feature they would like:
Dynamic USDT probe
  - node.js/java/language-foo can dynamically generate its own usdt
    symbol, and add a separate elf section on the fly
  - still working out what bcc instrumentation this needs, more in the


Kyle Laracey
Brenden Blanco
Deepa Kalani
Keith Burns
Jesper Brouer
Alban Crequy
Martin Lau
Brendan Gregg