linux-kernel - Re: [PATCH v2] irqchip/gic-v3-its: fix ITS queue timeout

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Date:   Sun, 10 Jun 2018 11:40:57 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Hanjun Guo <guohanjun@...wei.com>
Cc:     Yang Yingliang <yangyingliang@...wei.com>,
        <julien.thierry@....com>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] irqchip/gic-v3-its: fix ITS queue timeout


Hi Hanjun,

On Thu, 07 Jun 2018 13:25:26 +0100,
Hanjun Guo wrote:
> 
> Hi Marc,
> 
> On 2018/6/6 17:13, Marc Zyngier wrote:
> [...]
> > 
> > Wouldn't it be better to just return that the affinity setting request
> > is impossible to satisfy? And more to the point, how comes we end-up
> > in such a case?
> 
> The system is booted with a NUMA node has no memory attaching to it
> (memory-less NUMA node), also with NR_CPUS less than CPUs presented
> in MADT, so CPUs on this memory-less node are not brought up, and
> this NUMA node will not be online too. But the ITS attaching to this NUMA
> domain is still valid and represented via SRAT to ITS driver.
> 
> This is really the corner case which is triggered by the boot testing
> when enabling our D06 boards, but it's a bug :)

I'm not debating the bringing up (or lack thereof) of the secondary
CPUs. I'm questioning the affinity setting to unavailable CPUs, and I
really wonder what the semantic of such a thing is (and how we end-up
there).

Anyway, I'll plug the "SYNC to unmapped collection" issue (which
definitely needs fixing), but I'd like to understand the above.

Thanks,

	M.

-- 
Jazz is not dead, it just smell funny.