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Re: [PATCH] irqchip/gicv3-its: Enable cacheable attribute Read-allocate hints

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  Re: [PATCH] irqchip/gicv3-its: Enable cacheable attribute  Read-allocate hints Shanker Donthineni <shankerd@codeaurora.org> - 2016-08-29 17:40 +0200
    Re: [PATCH] irqchip/gicv3-its: Enable cacheable attribute  Read-allocate hints Marc Zyngier <marc.zyngier@arm.com> - 2016-08-30 10:50 +0200

#1471926 — Re: [PATCH] irqchip/gicv3-its: Enable cacheable attribute Read-allocate hints

Marc,

Are you planning to push this change? I talked to Qualcomm ITS hw team 
and they told me nice to have this change even though we see a small gain.

Shanker


On 07/12/2016 08:32 AM, Shanker Donthineni wrote:
> Hi Marc,
>
> On 07/12/2016 03:09 AM, Marc Zyngier wrote:
>> Hi Shanker,
>>
>> On 12/07/16 04:36, Shanker Donthineni wrote:
>>> Read-allocation hints are not enabled for both the GIC-ITS and GICR
>>> tables. This forces the hardware to always read the table contents
>>> from an external memory (DDR) which is slow compared to cache memory.
>>> Most of the tables are often read by hardware. So, it's better to
>>> enable Read-allocate hints in addition to Write-allocate hints in
>>> order to improve the GICR_PEND, GICR_PROP, Collection, Device, and
>>> vCPU tables lookup time.
>> While I'm not opposed to such a change, I'd like to see some evidence
>> that this actually makes a difference. Have you measured an improvement
>> on a particular implementation? If so, could you share your benchmarking
>> method so that it could be be measured on others as well?
> I have seen at least 5% performance gain when I was testing direct 
> VLPI feature
> on Qualcomm emulation platforms. On Silicon, this gain is not noticeable.
>
>
>> Thanks,
>>
>>     M.
>

-- 
Shanker Donthineni
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

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#1472326

On 29/08/16 16:35, Shanker Donthineni wrote:
> Marc,
> 
> Are you planning to push this change? I talked to Qualcomm ITS hw team 
> and they told me nice to have this change even though we see a small gain.

Hi Shanker,

As I asked before, I'd like to know what is the actual gain on real HW,
and how you measured it, so that I can try and make sure this doesn't
introduce regressions on other implementations. If it does, then we'll
probably have to quirk it.

Thanks,

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

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