[dpdk-dev] [PATCH v10 0/9] Add PMD power mgmt

[Liang, Ma]

On 28 Oct 21:27, Jerin Jacob wrote:
> On Wed, Oct 28, 2020 at 9:19 PM Ananyev, Konstantin
> <konstantin.ananyev at intel.com> wrote:
> > > > > > > 28/10/2020 14:49, Jerin Jacob:
> > > > > > > > On Wed, Oct 28, 2020 at 7:05 PM Liang, Ma <liang.j.ma at intel.com> wrote:
> > > > > > > > >
> > > > > > > > > Hi Thomas,
> > > > > > > > >   I think I addressed all of the questions in relation to V9. I don't think I can solve the issue of a generic API on my own. From the
> > > > > > > Community Call last week Jerin also said that a generic was investigated but that a single solution wasn't feasible.
> > > > > > > >
> > > > > > > > I think, From the architecture point of view, the specific
> > > > > > > > functionally of UMONITOR may not be abstracted.
> > > > > > > > But from the ethdev callback point of view, Can it be abstracted in
> > > > > > > > such a way that packet notification available through
> > > > > > > > checking interrupt status register or ring descriptor location, etc by
> > > > > > > > the driver. Use that callback as a notification mechanism rather
> > > > > > > > than defining a memory-based scheme that UMONITOR expects? or similar
> > > > > > > > thoughts on abstraction.
> > > > > >
> > > > > > I think there is probably some sort of misunderstanding.
> > > > > > This API is not about providing acync notification when next packet arrives.
> > > > > > This is about to putting core to sleep till some event (or timeout) happens.
> > > > > > From my perspective the closest analogy: cond_timedwait().
> > > > > > So we need PMD to tell us what will be the address of the condition variable
> > > > > > we should sleep on.
> > > > > >
> > > > > > > I agree with Jerin.
> > > > > > > The ethdev API is the blocking problem.
> > > > > > > First problem: it is not well explained in doxygen.
> > > > > > > Second problem: it is probably not generic enough (if we understand it well)
> > > > > >
> > > > > > It is an address to sleep(/wakeup) on, plus expected value.
> > > > > > Honestly, I can't think-up of anything even more generic then that.
> > > > > > If you guys have something particular in mind - please share.
> > > > >
> > > > > Current PMD callback:
> > > > > typedef int (*eth_get_wake_addr_t)(void *rxq, volatile void
> > > > > **tail_desc_addr, + uint64_t *expected, uint64_t *mask, uint8_t
> > > > > *data_sz);
> > > > >
> > > > > Can we make it as
> > > > > typedef void (*core_sleep_t)(void *rxq)
> > > > >
> > > > > if we do such abstraction and "move the polling on memory by HW/CPU"
> > > > > to the driver using a helper function then
> > > > > I can think of abstracting in some way in all PMDs.
> > > >
> > > > Ok I see, thanks for explanation.
> > > > From my perspective main disadvantage of such approach -
> > > > it can't be extended easily.
> > > > If/when will have an ability for core to sleep/wake-up on multiple events
> > > > (multiple addresses) will have to either rework that API again.
> > >
> > > I think, we can enumerate the policies and pass the associated
> > > structures as input to the driver.
> >
> > What I am trying to say: with that API we will not be able to wait
> > for events from multiple devices (HW queues).
> > I.E. something like that:
> >
> > get_wake_addr(port=X, ..., &addr[0], ...);
> > get_wake_addr(port=Y,..., &addr[1],...);
> > wait_on_multi(addr, 2);
> >
> > wouldn't be possible.
> 
> I see. But the current implementation dictates the only queue bound to
> a core. Right?
Current implementation only support 1:1 queue/core mapping is because of 
the limitation of umwait/umonitor which can not work with multiple address
range. However, for other scheme like PASUE/Freq Scale have no such limitation. 
The proposed API itself doesn't limit the 1:1 queue/core mapping. 
> 
> 
> >
> > >
> > >
> > > >
> > > > >
> > > > > Note: core_sleep_t can take some more arguments such as enumerated
> > > > > policy if something more needs to be pushed to the driver.
> > > > >
> > > > > Thoughts?
> > > > >
> > > > > >
> > > > > > >
> > > > > > > > > This API is experimental and other vendor support can be added as needed. If there are any other open issue let me know?
> > > > > > >
> > > > > > > Being experimental is not an excuse to throw something
> > > > > > > which is not satisfying.
> > > > > > >
> > > > > > >
> > > > > >