linux-kernel - Re: [PATCH] x86,cpu-hotplug: clear llc_shared

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Date:	Thu, 3 Jul 2014 11:51:35 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, toshi.kani@...com, imammedo@...hat.com,
	huawei.libin@...wei.com, paul.gortmaker@...driver.com,
	linux-kernel@...r.kernel.org, srivatsa.bhat@...ux.vnet.ibm.com
Subject: Re: [PATCH] x86,cpu-hotplug: clear llc_shared_mask at CPU hotplug

On Thu, Jul 03, 2014 at 01:52:52PM +0900, Yasuaki Ishimatsu wrote:
> I think that the reason to apply CPU number to ACPI ID is that CPU is
> used for the application without considering physical CPU. So even if
> CPU number is changed, it is no matter.

I don't think I understand what you're saying here...

> Thus the readded cores is numbered to unused CPU number.

Well, maybe we should use some method to number cores in a stable manner
so that they don't get new numbers when they reappear.

> I think the mask has 2 meanings as follows:
>   - representing CPUs that share same CPU cache.

... that share the last level cache.

>   - representing onlined CPUs

no, for that we have cpu_online_mask.

> So even if we keep their old numbers, we should clear the mask when
> offlinig CPU.

No, cpu_online_mask is for onlined cores. I think the mask which shows
which cores share a last level cache should not be changed *IF* the core
numbers remain stable, that is.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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