Should the kernel perf interface be available on autobuilders?

[Petter Reinholdtsen <pere@hungry.com>]

Hi.

Lluís Vilanova (cc) and I maintain the coz-profiler package in Debian,
and this package uses the perf kernel interface for profiling.  This
subsystem has received strict access limitations in recent Debian
kernels.  During build of the coz-profiler package it test itself to
ensure it is working, and this work on all autobuilders except one, the
x32 architecture.

Are the autobuilders expected to block access to the perf kernel
interface, or is this a misconfiguration of the x32 build host?

The reason I ask is that the restricted setting has changed in recent
years, and I expect all autobuilders to get the restricted setting of
x32 when they are upgraded.  I would prefer it to be defined that the
autobuilders should provide access to the perf interface during build.
This can be set by inserting a lower value in
/proc/sys/kernel/perf_event_paranoid, for example like this:

  echo 1 > /proc/sys/kernel/perf_event_paranoid

The default value in Jessie is 1 and this work with the coz-profiler
build, while the default value in unstable/testing is 3 and causes the
build to fail.  The details of this issue with coz-profiler can be found
in <URL: https://bugs.debian.org/844633 >.

Please CC us on any replies, as we are not subscribed to the
debian-wb-team@ mailing list.

-- 
Happy hacking
Petter Reinholdtsen