linux-kernel - Re: [PATCH v5 4/6] sched/isolation: Force housekeeping if isolcpus and nohz

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Message-ID: <aCxuIYqvbEn1xgmd@localhost.localdomain>
Date: Tue, 20 May 2025 13:57:21 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Gabriele Monaco <gmonaco@...hat.com>
Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Waiman Long <longman@...hat.com>
Subject: Re: [PATCH v5 4/6] sched/isolation: Force housekeeping if isolcpus
 and nohz_full don't leave any

Le Tue, May 20, 2025 at 01:17:20PM +0200, Gabriele Monaco a écrit :
> The isolcpus parameter can be used like:
> 1. isolcpus=1,2,3
> 2. isolcpus=domain,1,2,3
> 3. isolcpus=nohz,1,2,3
> 4. isolcpus=domain,nohz,1,2,3
> ...
> 
> 1 and 2 are equivalent (e.g. if no mode is specified, that's domain
> isolation), 3 is equivalent to nohz_full=1,2,3 and 4 is equivalent to
> 1-2 in combination with nohz_full=1,2,3
> 
> Now, the code takes into account that there are 2 arguments that can
> isolate (isolcpus and domain) and can be passed in any order, that
> specific code guards against those two passing inconsistent maps, e.g.:
> 
> 	isolcpus=nohz,0-4 nohz_full=5-8
> 
> Strictly speaking it's guarding for any other possible inconsistency
> but I believe that's the only one actually achievable.
> 
> Again, nothing forbids e.g.
> 
> 	isolcpus=domain,0-4 nohz_full=5-8
> 
> since they're different isolation flags and that's allowed (not sure if
> it really should be though).

Duh, yes, it only refuse if the flags are common and masks are different.
I seem to remember you already explained that to me last time and I already
slapped my forehead. Prepare for me to ask the same question one more time
in one week ;-)

-- 
Frederic Weisbecker
SUSE Labs