[dpdk-dev] [PATCH v5 00/23] Add DLB2 PMD

[Thomas Monjalon]

30/10/2020 16:35, McDaniel, Timothy:
> From: Thomas Monjalon <thomas at monjalon.net>
> > 30/10/2020 12:58, McDaniel, Timothy:
> > > From: McDaniel, Timothy
> > > > From: Thomas Monjalon <thomas at monjalon.net>
> > > > > 30/10/2020 10:43, Timothy McDaniel:
> > > > > > - note that the code still uses its private byte-encoded versions of
> > > > > >   umonitor/umwait, rather than the new functions in the power
> > > > > >   patch that are built on top of those intrinsics. This is intentional.
> > > > >
> > > > > Why? Now these intrinsics are available in the main branch.
> > > > > We should avoid duplicating such code.
> > > > >
> > > > >
> > > >
> > > > I had asked that the low level intrinsics (UMWAIT/UMONITOR) be split out so
> > > > that DLB/DLB2 could use them instead of its own private byte-encoded
> > versions,
> > > > but instead we have these wrappers that call the low level intrinsics. Those
> > > > wrappers
> > > > introduce additional overhead that is not required for DLB/DLB2. I have a
> > > > meeting with Ma Liang on Monday to discuss.
> > >
> > > I thought the ask of DLB was to just substitute the low level umwait/umonitor
> > byte
> > > encoded instructions DLB has defined privately with similar byte-encoded
> > instructions defined in the power
> > > patch. The power patch does not directly expose those, which is why I did not
> > update DLB/DLB2.
> > > The power patch does have the advantage of centralizing the race avoidance
> > > logic, which is a good thing for any PMD that wishes to take advantage of
> > umwait/umonitor.
> > 
> > So you mean the overhead is a good thing?
> > 
> > > Sorry for the confusion. I just misunderstood what was being asked of DLB in
> > regard to switching over..  That being said,
> > > I am willing to convert DLB/DLB2 to use  rte_power_monitor(...) in a future
> > patch-set.
> > 
> > Why not now?
> > 
> > Indeed there is a confusion and it looks like a lot of novlang
> > to exit from the situation.
> > We'll wait a clear decision with facts.
> > 
> 
> Hi Thomas,
> 
> I have updated DLB and DLB2 to use rte_power_monitor(...), and those patches are
> ready if you are willing to accept them and the 3 power patches.
> 
> For the sake of consistency, I see the benefit of using the power patch, even if it is 
> slightly less efficient that the DLB-specific implementation that I currently have.
> We have already encountered an empty queue, so this is no longer fast path for the PMD.

I am really concerned that the API in EAL is not the most efficient.
Why is that? Can we improve the EAL API?