[PATCH v9 1/3] power: add Intel uncore frequency control API to power library

[Hunt, David]

On 06/10/2022 18:32, Stephen Hemminger wrote:
> On Thu,  6 Oct 2022 09:38:01 +0000
> Tadhg Kearney <tadhg.kearney at intel.com> wrote:
>
>> Add API to allow uncore frequency adjustment. Uncore is a
>> term used by Intel to describe function of a microprocessor
>> that are closely connected to the core to achieve high
>> performance. This is done through manipulating related
>> uncore frequency control sysfs entries to adjust the
>> minimum and maximum uncore frequency values and works
>> on Linux for Intel hardware.
>>
>> Signed-off-by: Tadhg Kearney <tadhg.kearney at intel.com>
>> Reviewed-by: David Hunt <david.hunt at intel.com>
>> Acked-by: David Hunt <david.hunt at intel.com>


Hi Stephen,

> Looks like this is missing an opportunity for a more general
> long term solution in DPDK.


We're hoping that this is the first step along the path to that 
long-term solution. It's like the power library frequency control for 
cores, which was initially Intel only, and then more architectures were 
added over time. The API's are experimental, so can be adapted if needed.


> Shouldn't this be a general thing like the Linux kernel scheduler.

I don't think the kernel scheduler has any concept of uncore busyness, 
the uncore frequency is typically controlled by hardware, and if there's 
enough polling going on, the frequency of the uncore will remain high 
(if uncore frequency scaling is enabled). We're addressing that in this 
patch in that if the application realises that it's not processing a lot 
of packets even though most of it's cores are polling, it can tell the 
hardware to scale down the uncore to save power.


> Uncore is Intel specific, but there is already big/little cores
> on many ARM platforms.

I don't think big/little is related to uncore frequency scaling. The 
big/little cores still need to communicate via that architecture's 
communications bus (called uncore in Intel's case, though I've seen that 
term used on other architectures also). Where an architecture can scale 
the frequency of this communications bus, this patch set's functionality 
can be extended in the future to cover this.

Regards,
Dave