From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Xu <peterx@redhat.com>
Cc: Ming Lei <ming.lei@redhat.com>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Luiz Capitulino <lcapitulino@redhat.com>
Subject: Re: [PATCH V4] sched/isolation: isolate from handling managed interrupt
Date: Mon, 03 Feb 2020 23:15:50 +0000 [thread overview]
Message-ID: <87a75zz2hl.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20200203192154.GG155875@xz-x1>
Peter Xu <peterx@redhat.com> writes:
> The new "managed_irq" works for us, thanks for both of your work!
>
> However I just noticed that this new sub-parameter might break users
> if applied incorrectly to old kernels, because iiuc "isolcpus="
> parameter will not apply at all when there's unknown sub-parameters:
>
> static int __init housekeeping_isolcpus_setup(char *str)
> {
> unsigned int flags = 0;
>
> while (isalpha(*str)) {
> ...
> pr_warn("isolcpus: Error, unknown flag\n");
> return 0;
> }
> ...
> }
>
> Then the same kernel parameter will break isolcpus= if the user
> reboots and switches to an older kernel.
>
> A solution to this could be that we introduce an isolated parameter
> for "managed_irq", then on the old kernels only the new parameter will
> be ignored rather than the whole "isolcpus=" parameter, so nothing
> will break.
>
> I'm not sure whether it's already too late for this, or if there's any
> better alternative. Just raise this question up to see whether we
> still have chance to fix this up.
No, really. The basic guarantee is that your new kernel is going to work
fine with the previous command line, but making a guarantee that new
command line options still work on an old kernel are just creating a
horrible mess. So if that command line interface was not designed to
handle unknown arguments in the first place, you better fix that.
Thanks,
tglx
next prev parent reply other threads:[~2020-02-03 23:16 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-20 9:16 [PATCH V4] sched/isolation: isolate from handling managed interrupt Ming Lei
2020-01-22 13:25 ` Thomas Gleixner
2020-02-03 19:21 ` Peter Xu
2020-02-03 23:15 ` Thomas Gleixner [this message]
2020-02-03 23:57 ` Peter Xu
2020-02-04 9:13 ` Thomas Gleixner
2020-01-22 15:34 ` [tip: irq/core] genirq, sched/isolation: Isolate from handling managed interrupts tip-bot2 for Ming Lei
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