linux-kernel - Re: [RFC PATCH 0/4] add support for CommonLPIAff field

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Message-ID: <97382ff7-7f8f-f960-aa92-41a96c8e169f@arm.com>
Date:   Mon, 12 Mar 2018 12:25:02 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Yang Yingliang <yangyingliang@...wei.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/4] add support for CommonLPIAff field

On 12/03/18 12:13, Yang Yingliang wrote:
> 
> 
> On 2018/3/12 17:55, Marc Zyngier wrote:
>> On 12/03/18 06:49, Yang Yingliang wrote:
>>> This patch set adjust struct rdists to support CommonLPIAff field.
>>> This field is described in spec:
>>>
>>> CommonLPIAff, bits [25:24]
>>> The affinity level at which Redistributors share a LPI Configuration table.
>>> 00 All Redistributors must share a LPI Configuration table.
>>> 01 All Redistributors with the same Aff3 value must share an LPI Configurationt table.
>>> 10 All Redistributors with the same Aff3.Aff2 value must share an LPI Configuration table.
>>> 11 All Redistributors with the same Aff3.Aff2.Aff1 value must share an LPI Configuration
>>> table.
>>
>> What are you trying to achieve here? We already share the same
>> configuration table across all the redistributors, irrelevant the of
>> CommonLPIAff. Why would we need to do anything else?
> 
> In some cases, such as "with the same Aff3.Aff2 value must share an LPI
> Configuration table", redistributors will access local memory node
> only, it may improve the performance. And I don't have any beneficial
> data now. I may provide it later.

These are two different things.
- "must share" is what the kernel does *today*. No changes are required.
- NUMA behaviour has nothing to do with CommonLPIAff, and cannot be
based on that field.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...