[Click] Userlevel performance issues

Robert Ross rross at dsci.com
Thu Feb 7 09:43:54 EST 2008 

Do you know if this problem would affect kernel-mode performance as
well, or was this isolated to userlevel only?

On Tue, 2008-02-05 at 17:41, Eddie Kohler wrote:

> Hi Robert,
> 
> I wonder if your observed weirdness with LinkUnqueue was due to the 
> 100%-CPU-on-DelayUnqueue problem recently reported.  Maybe if you tried the 
> configuration now?
> 
> Eddie
> 
> 
> Robert Ross wrote:
> > I'm not sure what this means, but we have been able to completely avoid
> > this problem by using kernel-level Click with the experimental
> > FromUserDevice, and a user-level click reading FromDump and pushing
> > packets out on a custom ToRawFile element.
> > 
> > I will gladly put together and test a simple configuration.  It would be
> > identical to the configuration I had attached except for switching the
> > Socket() to a FromDump().  I will run some more tests and send you the
> > monitor.csv output from our script elements.  
> > 
> > BTW, we used the monitor.csv output file in tandem with the Java-based
> > LiveGraph to see real-time statistics on Click performance.  You can
> > also use Livegraph after the fact to open up and view our Monitor.csv
> > file on your end once I send you output.  It has been a very nice
> > marriage of capabilities for real-time analysis with minimal coding.
> > We've done something similar in kernel-level, but had to write a custom
> > java application to output the monitor.csv since kernel configurations
> > cannot output directly to files.
> > 
> > 
> > Robert Ross
> > DSCI Inc.
> > Office: 732.542.3113 x173
> > Home: 609.702.8114
> > Cell: 609.509.5139
> > Fax: 253.550.6198
> > 
> > -----Original Message-----
> > From: Eddie Kohler [mailto:kohler at cs.ucla.edu] 
> > Sent: Tuesday, January 29, 2008 2:39 PM
> > To: Robert Ross
> > Cc: Beyers Cronje; click at amsterdam.lcs.mit.edu
> > Subject: Re: [Click] Userlevel performance issues
> > 
> > Hi Robert,
> > 
> > The *job* of LinkUnqueue is specifically to throttle performance.  It is
> > designed to output packets at the bandwidth specified.  This will cause
> > a lower rate, pinned to that bandwidth!
> > 
> > The numbers you report are kind of reasonable.  Click parses bandwidths
> > as powers of 10, which is the networking standard as far as I can tell.
> > So 512Kbps = 512000bps = 64000Bps; 190p/s at this rate implies 336B
> > packets.  So 1360p/s, for your highest bandwidth LinkUnqueue, assuming
> > the same packet length, is roughly half what it "should" be.  That's not
> > great, but it's not terrible.
> > 
> > I have not run your configuration with Sockets, but I have with
> > InfiniteSources, and so forth, and have observed LinkUnqueue outputing
> > packets at the correct rate.  In fact I checked in an update to Counter,
> > to give it bit_rate and byte_rate handlers, making this easier to see.
> > 
> > LinkUnqueue should affect the upstream Socket elements only indirectly. 
> > LinkUnqueue stops pulling from its input when the emulated link is full.
> > This will cause an upstream Queue to fill up.  Some elements might
> > notice that Queue's full state and stop producing packets (since those
> > packets will only be dropped).  The InfiniteSource and user-level
> > FromHost elements have this behavior.  However, your use of
> > NotifierQueue (instead of Queue) would neutralize this effect, since
> > NotifierQueue doesn't provide full notification.
> > 
> > I am unsure in the end whether you are observing a bug or correct
> > behavior. 
> > Here are a couple questions to help us figure it out.
> > 
> > - Re: FromDump and ToDevice.  Can you reduce the configuration as much
> > as possible, and tell us what rates ToDevice achieves without FromDump,
> > and what it achieves with FromDump?  Your mail isn't specific about the
> > configuration or the performance numbers.
> > 
> > - Re: LinkUnqueue.  Can you send the output of your configuration (cool
> > use of define and Script btw), as well as the configuration?  Again,
> > with InfiniteSource I see expected behavior, and I would not expect
> > LinkUnqueue to throttle Socket.
> > 
> > It may be that you are finding an unfortunate interaction between
> > Click's task handlers and its file descriptor handlers -- something we
> > could potentially fix.  But without specific numbers it's hard to tell.
> > 
> > Eddie
> > 
> > 
> > Robert Ross wrote:
> >> The only clear item that seems to have a marked difference is the 
> >> LinkUnqueue element.  The fact that our ToDevice and FromDevice/Socket
> > 
> >> performance appears to be related somehow to the configuration of a 
> >> LinkUnqueue element sitting in the middle of our configuration is too 
> >> obvious to ignore.  Does LinkUnqueue perform some kind of 
> >> upstream/downstream notification to these elements, causing them to 
> >> throttle their behavior based on LinkUnqueue?
> >>  
> >> In our tests, with all other elements remaining the same, here is what
> > 
> >> we found from two independent read handler counts:
> >>  
> >> LinkUnqueue("512Kbps") = Maximum ~190 packets/second pushed from the 
> >> Socket element and pulled by the ToDevice element
> >> LinkUnqueue("1Mbps") = Maxmum ~290 packets/second pushed from the 
> >> Socket element and pulled by the ToDevice element
> >> LinkUnqueue("2Mbps") = Maximum ~490 packets/second pushed from the 
> >> Socket element and pulled by the ToDevice element
> >> LinkUnqueue("4Mbps") = Maximum ~780 packets/second pushed from the 
> >> Socket element and pulled by the ToDevice element
> >> LinkUnqueue("6Mbps") = Maximum ~980 packets/second pushed from the 
> >> Socket element and pulled by the ToDevice element
> >> LinkUnqueue("8Mbps") = Maximum ~1360 packets/second pushed from the 
> >> Socket element and pulled by the ToDevice element
> >>  
> >> It is also telling that independant handler counters corroborate 
> >> exactly the same maximum packets per second in two very different 
> >> places in the configuration.  Clearly you can see that the limitation 
> >> on processing is completely artificial and not an actual performance 
> >> problem, since increasing LinkUnqueue increases the performance in a 
> >> very controlled and obvious manner.
> >>  
> >> I have attached a simple configuration that examines specific handlers
> > 
> >> and outputs values each second to a CSV file for analysis.  The 
> >> configuration is scaled back to complete simplicity, yet has the same 
> >> performance as our actual configuration which has a much more 
> >> complicated configuration.  Nevertheless, the performance is identical
> > 
> >> and seems to point squarely at LinkUnqueue.
> >>  
> >> What is LinkUnqueue doing that could be causing this type of effect on
> > 
> >> FromHost, Socket and ToDevice?
> >>
> >>
> >> ________________________________
> >>
> >> From: Robert Ross
> >> Sent: Friday, January 25, 2008 7:40 PM
> >> To: 'Beyers Cronje'
> >> Cc: click at pdos.csail.mit.edu
> >> Subject: RE: [Click] Userlevel performance issues
> >>
> >>
> >> Sorry, I wasn't clear that the queues are necessary for our 
> >> configuration.  The configuration is somewhat complex.  I was only 
> >> attempting to highlight the important parts.
> >>  
> >>  
> >>
> >>
> >> ________________________________
> >>
> >> From: Beyers Cronje [mailto:bcronje at gmail.com]
> >> Sent: Friday, January 25, 2008 7:31 PM
> >> To: Robert Ross
> >> Cc: click at pdos.csail.mit.edu
> >> Subject: Re: [Click] Userlevel performance issues
> >>
> >>
> >> Hi Robert,
> >>
> >>
> >>  
> >>
> >> 	*       We first found that when UserLevel Click started pulling
> >> from a
> >> 	PCAP file, the performance of the ToDevice() appeared to drop 
> >> sharply.
> >> 	What I mean by this is that the ToDevice() pull handler reported
> > 
> >> values
> >> 	in the range of 200 packets/second once the PCAP file started 
> >> reading.
> >> 	This resulted in the outbound queue just prior to the ToDevice()
> > 
> >> filling
> >> 	up and eventually overflowing because the packet rate in the
> > PCAP 
> >> file
> >> 	is far more than 200 packets/second.
> >>
> >>
> >> You dont have to use a queue between FromDump and ToDevice as FromDump
> > 
> >> is an agnostic element. In other words you can connect Todevice 
> >> directly to FromDump which should ensure that at least no packets are 
> >> dropped and you should see best ToDevice performance.
> >>
> >> Also there are a few tuning parameters. Try tuning your NIC TX Ring 
> >> size. On the e1000 driver the default TX ring size is 256, experiment 
> >> with different value to see if it makes a difference.ToDevice uses a 
> >> packet socket from transmit, so it might be worth experimenting with 
> >> /proc/sys/net/core/wmem_default /proc/sys/net/core/wmem_max
> >>
> >>
> >> Beyers
> >>
> >>
> >>
> >> ----------------------------------------------------------------------
> >> --
> >>
> >> _______________________________________________
> >> click mailing list
> >> click at amsterdam.lcs.mit.edu
> >> https://amsterdam.lcs.mit.edu/mailman/listinfo/click

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