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

McDaniel, Timothy timothy.mcdaniel at intel.com
Fri Oct 30 16:35:17 CET 2020



> -----Original Message-----
> From: Thomas Monjalon <thomas at monjalon.net>
> Sent: Friday, October 30, 2020 8:15 AM
> To: McDaniel, Timothy <timothy.mcdaniel at intel.com>
> Cc: 'dev at dpdk.org' <dev at dpdk.org>; Carrillo, Erik G
> <erik.g.carrillo at intel.com>; Eads, Gage <gage.eads at intel.com>; Van Haaren,
> Harry <harry.van.haaren at intel.com>; 'jerinj at marvell.com'
> <jerinj at marvell.com>; 'david.marchand at redhat.com'
> <david.marchand at redhat.com>
> Subject: Re: [PATCH v5 00/23] Add DLB2 PMD
> 
> 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.




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