Re: DPDK and energy efficiency

[Robert Bays <robert () gdk org>]

To the nanog community, I’m sorry to have dragged this conversation out further.  I'm only responding to this because 
there are a significant number of open source projects and commercial products that use DPDK, or similar userspace 
network environment in their implementations.  The statements in this thread incorrectly cast them, because they use 
DPDK, as inefficient.  But the reality is they have all been designed from day one not to unnecessarily consume power.  
Please ask your open source dev and/or vendor of choice to verify.  But please don’t rely on the information in this 
thread to make decisions about what you deploy in your network.    

> On Feb 23, 2021, at 11:44 PM, Etienne-Victor Depasquale <edepa () ieee org> wrote:
>
> Hello Robert,
>
> Your statement that DPDK “keeps utilization at 100% regardless of packet activity” is just not correct.  You further 
> pre-suppose "widespread DPDK's core operating inefficiency” without any data to backup the operating inefficacy 
> assertion.  
>
> This statement is incorrect. 
> I have provided references (please see earlier e-mails) that investigate the operation of DPDK. 
> These references are items of peer-reviewed research that investigate a perceived problem with deployment of DPDK. 
> If the power consumption incurred while running DPDK were a corner case, 
> then there would be little to no research value in investigating such behavior.

Your references don’t take into account the code that this community would actually deploy; open source implementations 
like DANOS, FD.io <http://fd.io/>, or OVS.  They don’t audit any commercial products that implement userspace stacks.  
None of your references say that DPDK is inherently inefficient.  The closest they come is to say that tight polling is 
inefficient.  But tight polling, even in the earliest days of DPDK, was never meant to be a design pattern that was 
actually deployed into production.  I was there for those early conversations.

> Please don’t mislead the community into believing that DPDK == power bad
> I have to object to this statement. It does seem to imply malice, or, at best, amateurish behaviour, whether you 
> intended it or not.

Object all you want.  You are misleading people with your comments.  And in the process you are denigrating a large 
swath of OSS projects and commercial products that use DPDK.  Your survey questions are leading and provide a false 
dichotomy.  And when you post the results here, they will be archived forever to continue to spread misinformation, 
unfortunately.  

> Everything following is informational.  Stop here if so inclined.
>  Please stop delving into the detail of DPDK's facilities without regard for your logical omission: 
> that whether the facilities are available or not, DPDK's deployment profile (meaning: how it's being used in 
> general), as indicated by the references I've provided,
> are leading to high power inefficiency on cores partitioned to the data plane.

I’ve been writing network appliance code for over 20 years.  I designed network architectures for years before that.  I 
have 10s of thousands of DPDK based appliances in production at this moment across multiple different use cases. I work 
with companies that have 100s of thousands of units in production that leverage userspace runtimes.  I do think I 
understand DPDK’s deployment profile better than you.  That’s what I have been trying to tell you.  People don’t write 
inefficient DPDK code to put into production.  We’re not dumb.  We’ve been thinking about power consumption from day 
one.  DPDK was never supposed to be just a tight loop poll.  You were always supposed to put in the very minimal extra 
work to modulate power consumption.  

> The takeaway is that DPDK (and similar) doesn’t guarantee runaway power bills.
> Of course it doesn't. 
> Even the second question of that bare-bones survey tried to communicate this much.
>
> If you have questions, I’d be happy to discuss off line
> I would be happy to answer your objections in detail off line too.
> Just let me know.

Unfortunately, you don’t seem to be receptive to the numerous people contradicting your assertions.  So I’m out.  I’ll 
let my comments stand here.

> Cheers,
>
> Etienne
>
>
> On Wed, Feb 24, 2021 at 12:12 AM Robert Bays <robert () gdk org <mailto:robert () gdk org>> wrote:
> Hi Etienne,
>
> Your statement that DPDK “keeps utilization at 100% regardless of packet activity” is just not correct.  You further 
> pre-suppose "widespread DPDK's core operating inefficiency” without any data to backup the operating inefficacy 
> assertion.  Your statements, taken at face value, lead people to believe that if a project uses DPDK it’s going to 
> increase their power costs.  And that’s just not the case.  Please don’t mislead the community into believing that 
> DPDK == power bad.
>
> Everything following is informational.  Stop here if so inclined.
>
> DPDK does not dictate CPU utilization or power consumption, the application leveraging DPDK does.  It’s the 
> application that decides how to poll packets.  If an application implements DPDK using only a tight polling loop, 
> then it will keep CPU cores that are running DPDK threads at 100%.  But only the most simple and/or bespoke (think 
> trading) applications are implemented this way.  You don’t need tight polling all the time to get the performance 
> gains provided by DPDK or similar environments.  The vast majority of applications that this audience would actually 
> install in their networks do not do tight polling all the time and therefore don’t consume 100% of the CPU all the 
> time.   An interesting, helpful research effort you could lead would be to survey the ecosystem to catalog those 
> applications that do fall into the power hungry category and help them to change their code.  
>
> Intel DPDK application development guidelines don’t pre-suppose tight polling all the time and offer at least two 
> methods for optimizing power against throughput.  The older method is to use adaptive polling; increasing the polling 
> frequency as traffic load increases.  This keeps cpu utilization low when packet load is light and increases it as 
> traffic levels warrant.  The second method is to use P-states and/or C-states to put the processor into lower power 
> modes when traffic loads are lighter.  We have found that adaptive polling works better across a larger pool of 
> hardware types, and therefore that is what DANOS uses, amongst other things.  
>
> Further, performance and power consumption are dictated by a multivariate set of application decisions including: 
> design patterns such as single thread run to completion models vs. passing mbufs between multiple threads, buffer 
> sizes and cache management algorithms, combining and/or separating tx/rx threads, binding threads to specific lcores, 
> reserved cores for DPDK threads, hyperthreading, kernel schedulers, hypervisor schedulers, interface drivers, etc.  
> All of these are application specific, not DPDK generic.  Well written applications that leverage DPDK provide knobs 
> for the user to tune these settings for their specific environment and use case.  None of this unique to DPDK.  
> Solution designs were cribbed from previous technologies.
>
> The takeaway is that DPDK (and similar) doesn’t guarantee runaway power bills.  Power consumption is dictated by the 
> application.  Look for well behaved applications and everything will be alright.
>
> If you have questions, I’d be happy to discuss off line.
>
> Thanks,
> Robert.
>
>
> > On Feb 22, 2021, at 11:27 PM, Etienne-Victor Depasquale <edepa () ieee org <mailto:edepa () ieee org>> wrote:
> >
> > Sorry, last line should have been:
> > "intended to get an impression of how widespread ***knowledge of*** DPDK's core operating inefficiency is",
> > not:
> > "intended to get an impression of how widespread DPDK's core operating inefficiency is"
> >
> > On Tue, Feb 23, 2021 at 8:22 AM Etienne-Victor Depasquale <edepa () ieee org <mailto:edepa () ieee org>> wrote:
> > Beyond RX/TX CPU affinity, in DANOS you can further tune power consumption by changing the adaptive polling rate.  
> > It doesn’t, per the survey, "keep utilization at 100% regardless of packet activity.” 
> > Robert, you seem to be conflating DPDK 
> > with DANOS' power control algorithms that modulate DPDK's default behaviour.
> >
> > Let me know what you think; otherwise, I'm pretty confident that DPDK does:
> > "keep utilization at 100% regardless of packet activity.”   
> >
> > Keep in mind that this is a bare-bones survey intended for busy, knowledgeable people (the ones you'd find on 
> > NANOG) -
> > not a detailed breakdown of modes of operation of DPDK or DANOS.
> > DPDK has been designed for fast I/O that's unencumbered by the trappings of general-purpose OSes, 
> > and that's the impression that needs to be forefront.
> > Power control, as well as any other dimensions of modulation, 
> > are detailed modes of operation that are well beyond the scope of a bare-bones 2-question survey 
> > intended to get an impression of how widespread DPDK's core operating inefficiency is.
> >
> > Cheers,
> >
> > Etienne 
> >
> > On Mon, Feb 22, 2021 at 10:20 PM Robert Bays <robert () gdk org <mailto:robert () gdk org>> wrote:
> > Beyond RX/TX CPU affinity, in DANOS you can further tune power consumption by changing the adaptive polling rate.  
> > It doesn’t, per the survey, "keep utilization at 100% regardless of packet activity.”  Adaptive polling changes in 
> > DPDK optimize for tradeoffs between power consumption, latency/jitter and drops during throughput ramp up periods.  
> > Ideally your DPDK implementation has an algorithm that tries to automatically optimize based on current traffic 
> > patterns.
> >
> > In DANOS refer to the “system default dataplane power-profile” config command tree for adaptive polling settings.  
> > Interface RX/TX affinity is configured on a per interface basis under the “interfaces dataplane” config command 
> > tree.
> >
> > -robert
> >
> >
> > > On Feb 22, 2021, at 11:46 AM, Jared Geiger <jared () compuwizz net <mailto:jared () compuwizz net>> wrote:
> > >
> > > DANOS lets you specify how many dataplane cores you use versus control plane cores. So if you put a 16 core host 
> > > in to handle 2GB of traffic, you can adjust the dataplane worker cores as needed. Control plane cores don't stay 
> > > at 100% utilization. 
> > >
> > > I use that technique plus DANOS runs on VMware (not oversubscribed) which allows me to use the hardware for other 
> > > VMs. NICS are attached to the VM via PCI Passthrough which helps eliminate the overhead to the VMware hypervisor 
> > > itself.
> > >
> > > I have an 8 core VM with 4 cores set to dataplane and 4 to control plane. The 4 control plane cores are typically 
> > > idle only processing BGP route updates, SNMP, logs, etc.
> > >
> > > ~Jared
> > >
> > > On Sun, Feb 21, 2021 at 11:30 PM Etienne-Victor Depasquale <edepa () ieee org <mailto:edepa () ieee org>> wrote:
> > > Hello folks,
> > >
> > > I've just followed a thread regarding use of CGNAT and noted a suggestion (regarding DANOS) that includes use of 
> > > DPDK.
> > >
> > > As I'm interested in the breadth of adoption of DPDK, and as I'm a researcher into energy and power efficiency, 
> > > I'd love to hear your feedback on your use of power consumption control by DPDK.
> > >
> > > I've drawn up a bare-bones, 2-question survey at this link: 
> > >
> > > https://www.surveymonkey.com/r/J886DPY <https://www.surveymonkey.com/r/J886DPY>. 
> > >
> > > Responses have been set to anonymous.
> > >
> > > Cheers,
> > >
> > > Etienne
> > >
> > > -- 
> > > Ing. Etienne-Victor Depasquale
> > > Assistant Lecturer
> > > Department of Communications & Computer Engineering
> > > Faculty of Information & Communication Technology
> > > University of Malta
> > > Web. https://www.um.edu.mt/profile/etiennedepasquale <https://www.um.edu.mt/profile/etiennedepasquale>
> >
> >
> >
> > -- 
> > Ing. Etienne-Victor Depasquale
> > Assistant Lecturer
> > Department of Communications & Computer Engineering
> > Faculty of Information & Communication Technology
> > University of Malta
> > Web. https://www.um.edu.mt/profile/etiennedepasquale <https://www.um.edu.mt/profile/etiennedepasquale>
> >
> >
> > -- 
> > Ing. Etienne-Victor Depasquale
> > Assistant Lecturer
> > Department of Communications & Computer Engineering
> > Faculty of Information & Communication Technology
> > University of Malta
> > Web. https://www.um.edu.mt/profile/etiennedepasquale <https://www.um.edu.mt/profile/etiennedepasquale>
>
>
>
> -- 
> Ing. Etienne-Victor Depasquale
> Assistant Lecturer
> Department of Communications & Computer Engineering
> Faculty of Information & Communication Technology
> University of Malta
> Web. https://www.um.edu.mt/profile/etiennedepasquale <https://www.um.edu.mt/profile/etiennedepasquale>