[SRU][Jammy][PATCH 0/1] turbostat fails with too many open files on large systems

[Matthew Ruffell]

BugLink: https://bugs.launchpad.net/bugs/2069961

[Impact]

On large systems, e.g. with 512 cpus or more, turbostat fails to run due to
exceeding the rlimit for number of files. 512 cpus requires 1028 file
descriptors, but the current limit is 999.

$ lscpu
...
CPU(s):                  512
  On-line CPU(s) list:   0-511
...

$ sudo turbostat
...
turbostat: /sys/devices/system/cpu/cpu477/cpuidle/state0/usage: open failed: Too many open files

There is no workaround, apart from maybe using powerstat instead.

[Fix]

The fix is to increase the rlimit to increase the amount of file descriptors
that turbostat can open to 2^15, which should be plenty for some time to come.

commit 3ac1d14d0583a2de75d49a5234d767e2590384dd
Author: Wyes Karny <wyes.karny at amd.com>
Date:   Tue Oct 3 05:07:51 2023 +0000
Subject: tools/power turbostat: Increase the limit for fd opened
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3ac1d14d0583a2de75d49a5234d767e2590384dd

This landed in 6.9-rc4, and requires a backport for minor context adjustment in
the first hunk for jammy. Noble got fixed already through upstream stable.

[Testcase]

Deploy a bare metal system with 512 or more cpus.

Install linux-tools:

$ sudo apt install linux-tools-$(uname -r)

Run turbostat:

$ sudo turbostat
...
turbostat: /sys/devices/system/cpu/cpu477/cpuidle/state0/usage: open failed: Too many open files

There are test kernels available in the following ppa:

https://launchpad.net/~mruffell/+archive/ubuntu/sf388491-test

If you install them, you should be able to see normal turbostat output for all
cpus installed in the system.

[Where problems can occur]

We are simply increasing the rlimit for file descriptors that turbostat can
open. This should have no impact on any existing systems.

If a regression should occur, then turbostat functionality might not work.
Users could use powerstat instead as a workaround while things are fixed.

Wyes Karny (1):
  tools/power turbostat: Increase the limit for fd opened

 tools/power/x86/turbostat/turbostat.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

-- 
2.45.2