linux-kernel - Re: [PATCH] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters

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Message-ID: <20200214194008.GA1193332@xz-x1>
Date:   Fri, 14 Feb 2020 14:40:08 -0500
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Ming Lei <ming.lei@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sched/isolation: Allow "isolcpus=" to skip unknown
 sub-parameters

On Tue, Feb 04, 2020 at 11:16:39AM -0500, Peter Xu wrote:
> The "isolcpus=" parameter allows sub-parameters to exist before the
> cpulist is specified, and if it sees unknown sub-parameters the whole
> parameter will be ignored.  This design is incompatible with itself
> when we add more sub-parameters to "isolcpus=", because the old
> kernels will not recognize the new "isolcpus=" sub-parameters, then it
> will invalidate the whole parameter so the CPU isolation will not
> really take effect if we start to use the new sub-parameters while
> later we reboot into an old kernel. Instead we will see this when
> booting the old kernel:
> 
>     isolcpus: Error, unknown flag
> 
> The better and compatible way is to allow "isolcpus=" to skip unknown
> sub-parameters, so that even if we add new sub-parameters to it the
> old kernel will still be able to behave as usual even if with the new
> sub-parameter is specified.
> 
> Ideally this patch should be there when we introduce the first
> sub-parameter for "isolcpus=", so it's already a bit late.  However
> late is better than nothing.

Ping - Hi, Thomas, do you have any further comment on this patch?

Thanks,

-- 
Peter Xu