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

[Masoud Koleini <masoud.koleini@xxxxxxxxxxxxxxxx>]

On 10/01/15 18:39, Thomas Leonard wrote:
> On 18 December 2014 at 15:17, Masoud Koleini
> <masoud.koleini@xxxxxxxxxxxxxxxx> wrote:
> > On 18/12/14 13:19, Thomas Leonard wrote:
> > > 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.
> > > >
> > > > 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.)
> > > Do these traces show it after it stopped? The second has a long sleep,
> > > while the first looks like it was in the middle of a run.
> > >
> > > If it had stopped in both cases, it suggests that the whole unikernel
> > > stopped (not just the listen thread), because there are no more timer
> > > interrupts and no sleep region.
> > >
> > > Does "xl top" show the unikernel still using the CPU? Or it is
> > > waiting, or crashed?
> > >
> > > If you have a thread writing a string to the console once per second,
> > > does it continue after unikernel stops accepting frames?
> >   Yes, both are. It looks that I have more info on the traces with updated
> > Mirage libraries. So, I updated the traces in the repo.
> >
> > The unikernel is still working, as traces that periodically write info on
> > the console are still working too.
> I'm not sure, but it might be worth applying this fix and testing again:
>
>    https://github.com/mirage/mirage-net-xen/pull/16
>
> (when Netif stopped to wait for space in the transmit ring, it would
> sometimes fail to notice when space became available)
Great!

I found another issue in Netif receive thread "poll_thread". Inlarge 
transfers, thread stops receiving events when all the free space on the 
ring is filled and then rx_poll deallocates all the grant table indices:
https://github.com/mirage/mirage-net-xen/issues/15


> > With original configuration (netif unchanged), it looks that the reason is
> > unikernel gets out of memory after some time, while error message is shown
> > only in a few experiments. This is the main bottleneck for Mirage
> > applications,  which is waiting for a packet write to terminate is time
> > consuming and doesn't allow high rate packet switching for network
> > applications.
> >
> > Modifying netif by ignoring the thread that is waiting for the result of
> > writing to the ring is also problematic. So, any idea how to do bulk packet
> > write on a network interface?
> >
> >
> > > > 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
> > > >
> > > >
> > > > This message and any attachment are intended solely for the addressee and
> > > > may contain confidential information. If you have received this message
> > > > in
> > > > error, please send it back to me, and immediately delete it.   Please do
> > > > not
> > > > use, copy or disclose the information contained in this message or in any
> > > > attachment.  Any views or opinions expressed by the author of this email
> > > > do
> > > > not necessarily reflect the views of the University of Nottingham.
> > > >
> > > > This message has been checked for viruses but the contents of an
> > > > attachment
> > > > may still contain software viruses which could damage your computer
> > > > system,
> > > > you are advised to perform your own checks. Email communications with the
> > > > University of Nottingham may be monitored as permitted by UK legislation.
> >
> >
> >
> > This message and any attachment are intended solely for the addressee and
> > may contain confidential information. If you have received this message in
> > error, please send it back to me, and immediately delete it.   Please do not
> > use, copy or disclose the information contained in this message or in any
> > attachment.  Any views or opinions expressed by the author of this email do
> > not necessarily reflect the views of the University of Nottingham.
> >
> > This message has been checked for viruses but the contents of an attachment
> > may still contain software viruses which could damage your computer system,
> > you are advised to perform your own checks. Email communications with the
> > University of Nottingham may be monitored as permitted by UK legislation.




This message and any attachment are intended solely for the addressee
and may contain confidential information. If you have received this
message in error, please send it back to me, and immediately delete it. 

Please do not use, copy or disclose the information contained in this
message or in any attachment.  Any views or opinions expressed by the
author of this email do not necessarily reflect the views of the
University of Nottingham.

This message has been checked for viruses but the contents of an
attachment may still contain software viruses which could damage your
computer system, you are advised to perform your own checks. Email
communications with the University of Nottingham may be monitored as
permitted by UK legislation.


_______________________________________________
MirageOS-devel mailing list
MirageOS-devel@xxxxxxxxxxxxxxxxxxxx
http://lists.xenproject.org/cgi-bin/mailman/listinfo/mirageos-devel