[RFC PATCH 0/4] Add support for ARMv8.6 TWED feature

[Jingyi Wang]

Hi Marc，

I will consider more circumstances in the later test. Thanks for the
advice.

Thanks,
Jingyi


On 11/24/2020 7:02 PM, Marc Zyngier wrote:
> On 2020-11-13 07:54, Jingyi Wang wrote:
>> Hi all，
>>
>> Sorry for the delay. I have been testing the TWED feature performance
>> lately. We select unixbench as the benchmark for some items of it is
>> lock-intensive(fstime/fsbuffer/fsdisk). We run unixbench on a 4-VCPU
>> VM, and bind every two VCPUs on one PCPU. Fixed TWED value is used and
>> here is the result.
> 
> How representative is this?
> 
> TBH, I only know of two real world configurations: one where
> the vCPUs are pinned to different physical CPUs (and in this
> case your patch has absolutely no effect as long as there is
> no concurrent tasks), and one where there is oversubscription,
> and the scheduler moves things around as it sees fit, depending
> on the load.
> 
> Having two vCPUs pinned per CPU feels like a test that has been
> picked to give the result you wanted. I'd like to see the full
> picture, including the case that matters for current use cases.
> I'm specially interested in the cases where the system is
> oversubscribed, because TWED is definitely going to screw with
> the scheduler latency.
> 
> Thanks,
> 
>          M.