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

[Stephen Hemminger]

On Thu, 04 Jul 2024 16:14:42 +0200
Thomas Monjalon <thomas at 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.

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).