Re: [dpdk-dev] librte_power w/ intel_pstate cpufreq governor

["Zhang, Helin" <helin.zhang@intel.com>]

> -----Original Message-----
> From: Matthew Hall [mailto:mhall@mhcomputing.net]
> Sent: Thursday, January 14, 2016 3:04 PM
> To: Zhang, Helin
> Cc: dev@dpdk.org; Liang, Cunming; Zhou, Danny
> Subject: Re: [dpdk-dev] librte_power w/ intel_pstate cpufreq governor
> 
> On Tue, Jan 12, 2016 at 03:17:21PM +0000, Zhang, Helin wrote:
> > Hi Matthew
> >
> > Yes, you have indicated out the key, the power management module has
> changed or upgraded.
> > Could you help to try the legacy one to see if it still works, as indicated in
> your link?
> 
> I can do this, but according to the documents I am reading, the old Power
> Management module is secretly stubbed out / no-opped inside of the
> Skylake CPU core, and the core manages its own clockrate internally every 1
> msec instead of every 30 msec with input from the OS (Intel Speed Shift
> technology).
> 
> If this is true, then I suspect there is no point to getting it to work again with
> either the old frequency driver or the new driver, because the chip would
> not listen to it. So then it seems like it makes sense to skip the clock
> adjustment callbacks on Skylake and take extra stuff out of the fastpath code.
That's disappointing if Skylake is like that. Let's have a learning first, and then check if we can fix that.
But in addition, DPDK provide interrupt based packet receiving mechanism, can it be one of your choice?

For now, I am afraid that I don't have time on it, as we are all focusing on the next release development.
If no objection, I will find time later (may be in a month) to investigate that.
Of cause, please try to investigate that from your side.

> 
> > Taking control of the governor from kernel to user space, might need
> > one more checks before that. But it is actually not a big issue, as
> > user can switch it back to anything via 'echo'.
> 
> I think it's a bit bigger issue, as it leaves the chip in full-power mode without
> really warning anybody, instead of the standard default adaptive mode.
That's always there, for example, DPDK can exit accidently, without caring anything.
Then you can have the similar issue again.

> 
> > Yes, it seems that librte_power is out of date for a while. It is not
> > easy to track all the kernel versions. Now we have good chance to do
> > that, as you have reported issues. Let's have a look on the new power
> > management mechanism and then see if we can do something.
> 
> Yes, let me know how I could help. I don't know very much yet. My machine
> is Skylake Core i7-6700k. Unfortunately I think I am in trouble here, because
> there is no whitepaper on the Intel website for Intel Speed Shift technology
> at all.
It seems that you are so important for Intel. :) I don't have Skylake in hand. :(
Anyway, I will try to find time on that, and hopefully will find something or solution.
Thank you very much for the great jobs!

Regards,
Helin

> 
> > Really thanks to your questions!
> 
> I am looking forward to getting some answers figured out together.
> 
> > Regards,
> > Helin
> 
> Matthew.