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

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Message-ID: <20200309151917.GB4206@xz-x1>
Date:   Mon, 9 Mar 2020 11:19:17 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, 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>
Subject: Re: [PATCH] sched/isolation: Allow "isolcpus=" to skip unknown
 sub-parameters

On Fri, Feb 14, 2020 at 09:28:25PM +0100, Thomas Gleixner wrote:
> Peter Xu <peterx@...hat.com> writes:
> 
> > 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?
> 
> Fine with me.
> 
> Reviewed-by: Thomas Gleixner <tglx@...utronix.de>

Thanks Thomas!

Does anyone like to pick this up, or does this patch needs more
review?

Thanks,

-- 
Peter Xu