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

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Date:   Mon, 10 Jul 2017 15:51:53 +0530
From:   Ganapatrao Kulkarni <gpkulkarni@...il.com>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Shanker Donthineni <shankerd@...eaurora.org>,
        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 Marc,

On Mon, Jul 10, 2017 at 2:53 PM, Marc Zyngier <marc.zyngier@....com> wrote:
> On 10/07/17 10:08, Ganapatrao Kulkarni wrote:
>> On Mon, Jul 10, 2017 at 2:36 PM, Marc Zyngier <marc.zyngier@....com> wrote:
>>> On 10/07/17 09:48, Ganapatrao Kulkarni wrote:
>>>> Hi Marc,
>>>>
>>>> On Mon, Jul 3, 2017 at 8:23 PM, Marc Zyngier <marc.zyngier@....com> wrote:
>>>>> 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
>>>>
>>>> Did some measurement of interrupt response time for LPIs and we don't
>>>> see any major
>>>> improvement due to caching of Tables. However, we have seen
>>>> improvements of around 5%.
>>>
>>> An improvement of what exactly?
>>
>> interrupt response time.
>
> Measured how? On which HW? Using which benchmark?

This has been tested on ThunderX2.
We have instrumented gic-v3-its driver code to create dummy LPI device
with few vectors.
The LPI is induced from dummy device(through sysfs by writing to
TRANSLATOR reg).
The ISR routine(gic_handle_irq) being called to handle the induced LPI.
NODE 1 cpu is used to induce LPI and NODE 1 cpu/collection is mapped
in ITT to route this LPI.

CPU timer counter are sampled at the time LPI is Induced and in ISR
routine to calculate interrupt response time.
the result shown improvement of 5% with this patch.

Do you have any recommended benchmarks to test the same?

>
> Give me the actual benchmark results. Don't expect me to accept this
> kind of hand-wavy statement.
>
>         M.
> --
> Jazz is not dead. It just smells funny...

thanks
Ganapat