Re: [MirageOS-devel] Parallelizing writing to network devices

[Masoud Koleini <masoud.koleini@xxxxxxxxxxxxxxxx>]

> On 17 December 2014 at 18:05, Masoud Koleini<masoud.koleini@xxxxxxxxxxxxxxxx> 
> wrote:
> > Thanks Thomas for the great tracing tool!
> >
> > The following is a very simple unikernel with two interfaces, which
> > redirects frames captured on the first interface to the second one:
> >
> > https://github.com/koleini/parallelisation
> >
> > The problem is that in a high packet rate (more than 80'000 pps), switch
> > stops receiving. The goal is to spot the problem and enhance the throughput
> > of Mirage netif.
> I don't know if this is the problem, but in the code, I see you do:
>
>    listen if1 if2
>    >> (forward_thread if2)
>
> This ignores the result from listen, so if the listen thread later
> fails then the error will be discarded. I'd try something like this:
>
>    Lwt.choose [
>      listen if1 if2;
>      forward_thread if2
>    ]
>
> (and lose the "return" at the end of listen)
listen calls netif listen function, which only sets receive_callback on 
the interface (used by poll_thread). It looks that failing poll_thread 
is not monitored in netif code.

> I really think the >> operator should be banned...
>
> > Test environment consists of another vm running a traffic generator and
> > sending frames of a specific pattern (UDP frames of size 100 bytes) over the
> > bridge that connects to the first interface of the unikernel. Unikernel
> > forwards frames by collecting a number of frames from input queue and
> > running the same number of threads that write them to the output interface.
> >
> > Two trace files are uploaded to the repo. The first file is the output of
> > this configuration. This trace shows that each netif write locks until the
> > thread that writes on the front-end connection to the ring is returned
> > (function write_already_locked.)
> >
> > For the second trace, the return of the thread is ignored (commenting out
> > "lwt () = th in" in write_already_locked). This considerably increases
> > switching speed, but after some running time, it looks that after garbage
> > collection, similar problem happens.
> >
> > Thomas and Anil, any idea from given traces, and how it is possible to make
> > the traces more informative?
> >
> > Thanks.
> >
> >
> > On 28/11/14 16:55, Thomas Leonard wrote:
> > > On 28 November 2014 at 16:24, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
> > > > > On 28 Nov 2014, at 16:03, Masoud Koleini
> > > > > <masoud.koleini@xxxxxxxxxxxxxxxx> wrote:
> > > > >
> > > > > Thanks Anil.
> > > > >
> > > > > > - graph the ring utilisation to see if it's always full (Thomas
> > > > > > Leonard's profiling patches should help here)
> > > > > Would you please point me out to the profiling patches?
> > > > See:
> > > > http://roscidus.com/blog/blog/2014/10/27/visualising-an-asynchronous-monad/
> > > The installation instructions here are for the previous version
> > > (though they should still work). If you want to try the latest
> > > version, the current Git mirage allows you to pass a ~tracing argument
> > > to "register" in your config.ml, e.g.
> > >
> > > let tracing = mprof_trace ~size:1000000 () in
> > > register "myunikernel" ~tracing [
> > >     main $ ...
> > > ]
> > >
> > > This uses a newer version of the profiling API. You should generally
> > > "opam pin" the #tracing2 branches rather than #tracing to use it.
> > >
> > > Note also that it doesn't currently record ring utilisation, so you'll
> > > still need to do some work to get that. You could use the
> > > MProf.Counter interface, in which case the GUI will display it as a
> > > graph over the trace.
> > >
> > > > > > - try to reduce the parallelisation to see if some condition there
> > > > > > alleviates the issue to track it down.
> > > > > Reducing the maximum number of threads running in parallel reduced CPU
> > > > > utilization, and vm was functioning for a much longer time, but the same
> > > > > problem occurred at the end.
> > > > >
> > > > > It might be more useful looking at the code. Please have a look at the
> > > > > function "f_thread" in the file uploaded on the following repo:
> > > > >
> > > > > https://github.com/koleini/parallelisation
> > > > That's a lot of code to try and distill down a test case.  Try to cut it
> > > > down significantly by building a minimal Ethernet traffic generator that
> > > > outputs frames with a predictable pattern in the frame, and a receiver that
> > > > will check that the pattern is received as expected.
> > > >
> > > > Then you can try out your parallel algorithm variations on the simple
> > > > Ethernet sender/receiver and narrow down the problem without all the other
> > > > concerns.
> > > >
> > > > Once the bug is tracked down, we can add the sender/receiver into
> > > > mirage-skeleton and use it as a test case to ensure that this functional
> > > > never regresses in the future.  Line rate Ethernet transmission has worked
> > > > in the past, but we never added a test case to ensure it stays working.
> > > >
> > > > Anil
> > > > _______________________________________________
> > > > MirageOS-devel mailing list
> > > > MirageOS-devel@xxxxxxxxxxxxxxxxxxxx
> > > > http://lists.xenproject.org/cgi-bin/mailman/listinfo/mirageos-devel
> >
> >
> >
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