Re: [PATCH v2 2/2] eal: add Arm WFET in power management intrinsics

[Thomas Monjalon <thomas@monjalon.net>]

04/07/2024 16:55, Stephen Hemminger:
> On Thu, 04 Jul 2024 16:14:42 +0200
> Thomas Monjalon <thomas@monjalon.net> wrote:
> 
> > > > Let’s ask Pavan why this flag is used in cn10k driver.
> > > > 
> > > > From our perspective, WFE is available on all the supported arm platforms in
> > > > DPDK.
> > > > Therefore, RTE_ARM_USE_WFE should be treated as a flag to choose between
> > > > WFE
> > > > and non-WFE code paths due to performance reasons rather than as a flag
> > > > that indicates
> > > > the availability of the instruction on the target CPU.
> > > >   
> > > 
> > > We are using this flag to allow application to choose between WFE and non-WFE code path.
> > > The non-WFE path performs slightly better.  
> > 
> > What's the benefit of the WFE path then?
> 
> WFE saves power at the expense of latency.

Yes maybe there is a misunderstanding.
Pavan can you confirm you were saying "throughput is better on non-WFE"?
but "power consumption is lower on WFE path"?

> Maybe some form of hybrid approach would work best and could
> be always used.
> 
> For example, many implementations of mutex do a short spin poll
> then fall back to a waiting primitive (like futex).