Re: [dpdk-dev] [PATCH] doc: fix guide for DLB v2.5

[David Marchand <david.marchand@redhat.com>]

On Mon, May 17, 2021 at 3:48 PM McDaniel, Timothy
<timothy.mcdaniel@intel.com> wrote:
> > > @@ -387,4 +366,17 @@ Class of service can be specified in the devargs, as
> > follows
> > >
> > >      .. code-block:: console
> > >
> > > -       --vdev=dlb2_event,cos=<0..4>
> > > +       --allow ea:00.0,cos=<0..4>
> > > +
> > > +Use X86 Vector Instructions
> > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > +
> > > +DLB supports using x86 vector instructions to optimize the data path.
> > > +
> > > +The default mode of operation is to use scalar instructions, but
> > > +the use of vector instructions can be enabled in the devargs, as
> > > +follows
> > > +
> > > +    .. code-block:: console
> > > +
> > > +       --allow ea:00.0,vector_opts_enabled=<y/Y>
> >
> > This option does not exist.
> > All I see is:
> > drivers/event/dlb2/dlb2_priv.h:#define DLB2_VECTOR_OPTS_DISAB_ARG
> > "vector_opts_disable"
> >
>
> The option name changed with patch 93235/16973 "[1/1] event/dlb2: fix vector based dequeue", which
> is currently out for review. That patch fixed a couple of recently discovered issues in the vector path, so to be safe
> we changed the default from running with the vector dequeue optimizations to running with the scalar dequeue
> implementation.

I see Thomas had comments on this patch that changes the option (among
other things).
The documentation update for this option should go at the same time it
is introduced/renamed.


>
> > What of --force-max-simd-bitwidth ?
>
> The intent of the " vector_opts_enabled" switch is to allow experimentally enabled the vector based
> implementation, not to indicate whether those instructions are supported or not on the target platform.

The commit 000a7b8e7582 ("event/dlb2: optimize dequeue operation")
already had the issue: the event/dlb2 driver ignores the global knob
on activating vector stuff.


-- 
David Marchand