[ovs-dev] [PATCH v6 6/6] docs/dpdk/bridge: add datapath performance section.

Fri Jul 10 17:11:24 UTC 2020

> -----Original Message-----
> From: Stokes, Ian <ian.stokes at intel.com>
> Sent: Friday, July 10, 2020 5:00 PM
> To: Van Haaren, Harry <harry.van.haaren at intel.com>; ovs-dev at openvswitch.org
> Cc: i.maximets at ovn.org; u9012063 at gmail.com; fiezzi at redhat.com
> Subject: Re: [PATCH v6 6/6] docs/dpdk/bridge: add datapath performance
> section.
> 
> 
> 
> On 7/2/2020 6:43 PM, Harry van Haaren wrote:
> > This commit adds a section to the dpdk/bridge.rst netdev documentation,
> > detailing the added DPCLS functionality. The newly added commands are
> > documented, and sample output is provided.
> >
> > Running the DPCLS autovalidator with unit tests by default is possible
> > through re-compiling the autovalidator to have the highest priority at
> > startup time. This avoids making changes to all tests, and enables
> > debug and CI builds to validate every lookup implementation with all
> > unit tests.
> >
> > Add NEWS updates for CPU ISA, dynamic subtables, and AVX512 lookup.
> >
> > Signed-off-by: Harry van Haaren <harry.van.haaren at intel.com>
> >
> 
> Hi Harry,
> What you have below looks good to me.
> 
> The only additional ideas that might be worth adding would be either
> validated compilers as mention in patch 1 f the series (maybe this is
> not needed, but reviewing the existing Compilation section for OVS
> already states a GCC version that was tested with OVS DPDK so at least 1
> known GCC version is provided).

As mentioned in reply to first patch, I don't see value in stating what compilers
work or don’t - we must just rely on compilers working. OVS can recommend
or state that it is tested with specific compilers - but that is an independent 
issue to this patchset.

> Noting the configure, make CFLAGS dependency might be of use too
> although again, depends on how people configure and compile OVS to date.

Examples commands and documentation added to remedy this.

> Lastly possibly adding a section on what to check if AVX512 lookup is
> not appearing might be useful also.

Added section on potential issues regarding binutils bug, and how to
remedy.

> BR
> Ian

Thanks for review, -Harry

> >
> > v5:
> > - Include NEWS item updates.
> >
> > v4:
> > - Fix typos (William Tu)
> > - Update get commands to use include "prio" as updated in v4
> > - Add section on enabling autovalidator by default for unit tests
> > ---
> >   Documentation/topics/dpdk/bridge.rst | 77 ++++++++++++++++++++++++++++
> >   NEWS                                 |  3 ++
> >   2 files changed, 80 insertions(+)
> >
> > diff --git a/Documentation/topics/dpdk/bridge.rst
> b/Documentation/topics/dpdk/bridge.rst
> > index f0ef42ecc..526d5c959 100644
> > --- a/Documentation/topics/dpdk/bridge.rst
> > +++ b/Documentation/topics/dpdk/bridge.rst
> > @@ -137,3 +137,80 @@ currently turned off by default.
> >   To turn on SMC::
> >
> >       $ ovs-vsctl --no-wait set Open_vSwitch . other_config:smc-enable=true
> > +
> > +Datapath Classifier Performance
> > +-------------------------------
> > +
> > +The datapath classifier (dpcls) performs wildcard rule matching, a compute
> > +intensive process of matching a packet ``miniflow`` to a rule ``miniflow``. The
> > +code that does this compute work impacts datapath performance, and
> optimizing
> > +it can provide higher switching performance.
> > +
> > +Modern CPUs provide extensive SIMD instructions which can be used to get
> higher
> > +performance. The CPU OVS is being deployed on must be capable of running
> these
> > +SIMD instructions in order to take advantage of the performance benefits.
> > +In OVS v2.14 runtime CPU detection was introduced to enable identifying if
> > +these CPU ISA additions are available, and to allow the user to enable them.
> > +
> > +OVS provides multiple implementations of dpcls. The following command
> enables
> > +the user to check what implementations are available in a running instance ::
> > +
> > +    $ ovs-appctl dpif-netdev/subtable-lookup-prio-get
> > +    Available lookup functions (priority : name)
> > +            0 : autovalidator
> > +            1 : generic
> > +            0 : avx512_gather
> > +
> > +To set the priority of a lookup function, run the ``prio-set`` command ::
> > +
> > +    $ ovs-appctl dpif-netdev/subtable-lookup-prio-set avx512_gather 5
> > +    Lookup priority change affected 1 dpcls ports and 1 subtables.
> > +
> > +The highest priority lookup function is used for classification, and the output
> > +above indicates that one subtable of one DPCLS port is has changed its lookup
> > +function due to the command being run. To verify the prioritization, re-run
> the
> > +get command, note the updated priority of the ``avx512_gather`` function ::
> > +
> > +    $ ovs-appctl dpif-netdev/subtable-lookup-prio-get
> > +    Available lookup functions (priority : name)
> > +            0 : autovalidator
> > +            1 : generic
> > +            5 : avx512_gather
> > +
> > +If two lookup functions have the same priority, the first one in the list is
> > +chosen, and the 2nd occurance of that priority is not used. Put in logical
> > +terms, a subtable is chosen if its priority is greater than the previous
> > +best candidate.
> > +
> > +CPU ISA Testing and Validation
> > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > +
> > +As multiple versions of DPCLS can co-exist, each with different CPU ISA
> > +optimizations, it is important to validate that they all give the exact same
> > +results. To easily test all DPCLS implementations, an ``autovalidator``
> > +implementation of the DPCLS exists. This implementation runs all other
> > +available DPCLS implementations, and verifies that the results are identical.
> > +
> > +Running the OVS unit tests with the autovalidator enabled ensures all
> > +implementations provide the same results. Note that the performance of the
> > +autovalidator is lower than all other implementations, as it tests the scalar
> > +implementation against itself, and against all other enabled DPCLS
> > +implementations.
> > +
> > +To adjust the DPCLS autovalidator priority, use this command ::
> > +
> > +    $ ovs-appctl dpif-netdev/subtable-lookup-prio-set autovalidator 7
> > +
> > +Running Unit Tests with Autovalidator
> > ++++++++++++++++++++++++++++++++++++++
> > +
> > +To run the OVS unit test suite with the DPCLS autovalidator as the default
> > +implementation, it is required to recompile OVS. During the recompilation,
> > +the default priority of the `autovalidator` implementation is set to the
> > +maximum priority, ensuring every test will be run with every lookup
> > +implementation ::
> > +
> > +    $ ./configure --enable-autovalidator
> > +
> > +Compile OVS in debug mode to have `ovs_assert` statements error out if
> > +there is a mis-match in the DPCLS lookup implementation.
> > diff --git a/NEWS b/NEWS
> > index 0116b3ea0..da8725b59 100644
> > --- a/NEWS
> > +++ b/NEWS
> > @@ -20,6 +20,9 @@ Post-v2.13.0
> >        * New configuration knob 'other_config:lb-output-action' for bond ports
> >          that enables new datapath action 'lb_output' to avoid recirculation
> >          in balance-tcp mode.  Disabled by default.
> > +     * Add runtime CPU ISA detection to allow optimized ISA functions
> > +     * Add support for dynamically changing DPCLS subtable lookup functions
> > +     * Add ISA optimized DPCLS lookup function using AVX512
> >      - Tunnels: TC Flower offload
> >        * Tunnel Local endpoint address masked match are supported.
> >        * Tunnel Romte endpoint address masked match are supported.
> >