[Bug 2069961] Re: turbostat fails with too many open files on large systems

This bug is awaiting verification that the linux-mtk/5.15.0-1036.43
kernel in -proposed solves the problem. Please test the kernel and
update this bug with the results. If the problem is solved, change the
tag 'verification-needed-jammy-linux-mtk' to 'verification-done-jammy-
linux-mtk'. If the problem still exists, change the tag 'verification-
needed-jammy-linux-mtk' to 'verification-failed-jammy-linux-mtk'.


If verification is not done by 5 working days from today, this fix will
be dropped from the source code, and this bug will be closed.


See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how
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** Tags added: kernel-spammed-jammy-linux-mtk-v2 verification-needed-jammy-linux-mtk

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

Title:
turbostat fails with too many open files on large systems

Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Jammy:
Fix Released
Status in linux source package in Mantic:
Won't Fix
Status in linux source package in Noble:
Fix Released

Bug description:
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@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.

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