linux-kernel - Re: [PATCH] irqchip: gicv3-its: Use NUMA aware memory allocation for ITS tables

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Message-ID: <27b46938-ae23-9750-e0c7-09fa472d3297@arm.com>
Date:   Mon, 3 Jul 2017 15:53:49 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     shankerd@...eaurora.org, Ganapatrao Kulkarni <gpkulkarni@...il.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Vikram Sethi <vikrams@...eaurora.org>,
        Jayachandran C <jnair@...iumnetworks.com>,
        "ganapatrao.kulkarni@...ium.com" <ganapatrao.kulkarni@...ium.com>
Subject: Re: [PATCH] irqchip: gicv3-its: Use NUMA aware memory allocation for
 ITS tables

Hi Shanker,

On 03/07/17 15:24, Shanker Donthineni wrote:
> Hi Marc,
> 
> On 06/30/2017 03:51 AM, Marc Zyngier wrote:
>> On 30/06/17 04:01, Ganapatrao Kulkarni wrote:
>>> On Fri, Jun 30, 2017 at 8:04 AM, Ganapatrao Kulkarni
>>> <gpkulkarni@...il.com> wrote:
>>>> Hi Shanker,
>>>>
>>>> On Sun, Jun 25, 2017 at 9:16 PM, Shanker Donthineni
>>>> <shankerd@...eaurora.org> wrote:
>>>>> The NUMA node information is visible to ITS driver but not being used
>>>>> other than handling errata. This patch allocates the memory for ITS
>>>>> tables from the corresponding NUMA node using the appropriate NUMA
>>>>> aware functions.
>>>
>>> IMHO, the description would have been more constructive?
>>>
>>> "All ITS tables are mapped by default to NODE 0 memory.
>>> Adding changes to allocate memory from respective NUMA NODES of ITS devices.
>>> This will optimize tables access and avoids unnecessary inter-node traffic."
>>
>> But more importantly, I'd like to see figures showing the actual benefit
>> of this per-node allocation. Given that both of you guys have access to
>> such platforms, please show me the numbers!
>>
> 
> I'll share the actual results which shows the improvement whenever 
> available on our next chips. Current version of Qualcomm qdf2400 doesn't 
> support multi socket configuration to capture results and share with you. 
> 
> Do you see any other issues with this patch apart from the performance 
> improvements. I strongly believe this brings the noticeable improvement 
> in numbers on systems where it has multi node memory/CPU configuration.

I agree that it *could* show an improvement, but it very much depends on
how often the ITS misses in its caches. For this kind of patches, I want
to see two things:

1) It brings a measurable benefit on NUMA platforms
2) it doesn't adversely impact non-NUMA systems

I can deal with (2), but I have no way of evaluating (1), mostly for the
lack of an infrastructure exercising multiple ITSs at the same time.

Thanks,

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