[ovs-dev] [PATCH] dpif-netdev: Report overhead busy cycles per pmd.

[David Marchand]

On Thu, Jun 10, 2021 at 3:37 PM Aaron Conole <aconole at redhat.com> wrote:
>
> Hi David,
>
> David Marchand <david.marchand at redhat.com> writes:
>
> > When setting PMD auto load balance parameters and observing the
> > feature (and the per rxq statistics) in action, you can easily get
> > rebalances while the sum of per rxq pmd usage is below the pmd load
> > threshold you had set.
> >
> > This is because the dpif-netdev/pmd-rxq-show command only reports "pure"
> > rxq cycles while some cycles are used in the pmd mainloop and adds up to
> > the total pmd load.
> >
> > dpif-netdev/pmd-stats-show does report per pmd load usage.
> > This load is measured since the last dpif-netdev/pmd-stats-clear call.
> > On the other hand, the auto load balance feature uses the pmd load on a 10s
> > sliding window which makes it non trivial to correlate.
> >
> > Gather per pmd busy cycles with the same periodicity and report the
> > difference as overhead in dpif-netdev/pmd-rxq-show so that we have all
> > info in a single command.
> >
> > Example:
> > $ ovs-appctl dpif-netdev/pmd-rxq-show
> > pmd thread numa_id 0 core_id 4:
> >   isolated : false
> >   port: dpdk0             queue-id:  0 (enabled)   pmd usage: 37 %
> >   port: dpdk1             queue-id:  0 (enabled)   pmd usage: 36 %
> >   port: vhost3            queue-id:  0 (enabled)   pmd usage:  0 %
> >   port: vhost6            queue-id:  0 (enabled)   pmd usage:  0 %
> >   port: vhost7            queue-id:  0 (enabled)   pmd usage:  0 %
> >   overhead:  4 %
> > pmd thread numa_id 0 core_id 18:
> >   isolated : false
> >   port: vhost0            queue-id:  0 (enabled)   pmd usage: 37 %
> >   port: vhost1            queue-id:  0 (enabled)   pmd usage: 39 %
> >   port: vhost2            queue-id:  0 (enabled)   pmd usage:  0 %
> >   port: vhost4            queue-id:  0 (enabled)   pmd usage:  0 %
> >   port: vhost5            queue-id:  0 (enabled)   pmd usage:  0 %
> >   overhead:  5 %
> >
> > Signed-off-by: David Marchand <david.marchand at redhat.com>
> > ---
>
> ... snip ...
>
> > diff --git a/tests/pmd.at b/tests/pmd.at
> > index cc5371d5a5..256adb83f0 100644
> > --- a/tests/pmd.at
> > +++ b/tests/pmd.at
> > @@ -72,6 +72,7 @@ CHECK_PMD_THREADS_CREATED()
> >  AT_CHECK([ovs-appctl dpif-netdev/pmd-rxq-show | sed SED_NUMA_CORE_PATTERN], [0], [dnl
> >  pmd thread numa_id <cleared> core_id <cleared>:
> >    isolated : false
> > +  usage: NOT AVAIL
>
> I don't see this added anywhere, but I do see "overhead:" added.  I
> guess this is leftover from an earlier version.  It causes test case failures.

Errr, yes.
Kevin also reported it offlist.
I'll send v2 after retesting unit test..

Thanks.


-- 
David Marchand