linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Chris Friesen <chris.friesen@windriver.com>
To: Frederic Weisbecker <frederic@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: question about isolcpus and nohz_full
Date: Thu, 9 Sep 2021 10:26:04 -0600	[thread overview]
Message-ID: <b39eca5b-98e4-6b9e-c65b-63aad84d8caf@windriver.com> (raw)

Hi,

I'm finally getting around to moving to a newer kernel, and I'm running 
into a warning "Housekeeping: nohz_full= must match isolcpus=".

In my environment I had a number of "fully-isolated" CPUs with both 
"isolcpus" and "nohz_full", then a number of less-isolated CPUs that had 
"nohz_full" enabled but not "isolcpus", then the housekeeping CPUs.  It 
appears this is no longer supported via the boot args.  (The 
"less-isolated CPUs were used for applications that expected the usual 
load balancing from the scheduler but didn't want to be interrupted by 
timer ticks.)

1) The kernel-parameters documentation for "isolcpus=" doesn't say 
anything about needing to match "nohz_full", nor does the documentation 
for "nohz_full" mention that it needs to align with "isolcpus".  Maybe 
this would be a good thing to add?

2) Is it allowed to specify  "nohz_full" for some CPUs at boot time 
without specifying any isolcpus?  If so, what happens if I later isolate 
a subset of those CPUs using "cpuset.sched_load_balance" in cgroups?  Is 
that allowed when the equivalent boot args are not?

Thanks,

Chris


             reply	other threads:[~2021-09-09 16:26 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-09 16:26 Chris Friesen [this message]
2021-09-10  4:14 ` question about isolcpus and nohz_full Mike Galbraith

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=b39eca5b-98e4-6b9e-c65b-63aad84d8caf@windriver.com \
    --to=chris.friesen@windriver.com \
    --cc=frederic@kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).