Re: [dpdk-dev] [PATCH v2] doc: add preferred burst size support

[Bruce Richardson <bruce.richardson@intel.com>]

On Thu, Feb 01, 2018 at 07:58:32PM +0530, Shreyansh Jain wrote:
> On Thursday 01 February 2018 06:57 PM, Bruce Richardson wrote:
> > On Thu, Feb 01, 2018 at 06:18:23PM +0530, Shreyansh Jain wrote:
> > > rte_eth_rx_burst(..,nb_pkts) function has semantic that if return value
> > > is smaller than requested, application can consider it end of packet
> > > stream. Some hardware can only support smaller burst sizes which need
> > > to be advertised. Similar is the case for Tx burst.
> > > 
> > > This patch adds deprecation notice for rte_eth_dev_info structure as
> > > two new members, for preferred Rx and Tx burst size would be added -
> > > impacting the size of the structure.
> > > 
> > > Signed-off-by: Shreyansh Jain <shreyansh.jain@nxp.com>
> > > ---
> > > * Refer: http://dpdk.org/dev/patchwork/patch/32112 for context
> > > 
> > > v2:
> > >   - fix spelling error in deprecation notice
> > > 
> > >   doc/guides/rel_notes/deprecation.rst | 8 ++++++++
> > >   1 file changed, 8 insertions(+)
> > > 
> > > diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
> > > index d59ad5988..fdc7656fa 100644
> > > --- a/doc/guides/rel_notes/deprecation.rst
> > > +++ b/doc/guides/rel_notes/deprecation.rst
> > > @@ -59,3 +59,11 @@ Deprecation Notices
> > >     be added between the producer and consumer structures. The size of the
> > >     structure and the offset of the fields will remain the same on
> > >     platforms with 64B cache line, but will change on other platforms.
> > > +
> > > +* ethdev:  Currently, if the  rte_eth_rx_burst() function returns a value less
> > > +  than *nb_pkts*, the application will assume that no more packets are present.
> > > +  Some of the hw queue based hardware can only support smaller burst for RX
> > > +  and TX and thus break the expectation of the rx_burst API. Similar is the
> > > +  case for TX burst. ``rte_eth_dev_info`` will be added with two new
> > > +  parameters, ``uint16_t pref_rx_burst`` and ``uint16_t pref_tx_burst``,
> > > +  for preferred RX and TX burst sizes, respectively.
> > > -- 
> > > 2.14.1
> > > 
> > 
> > LTGM as far as it goes, but following discussion on this patch,
> > http://dpdk.org/ml/archives/dev/2018-January/089585.html
> > I think we might also want to add in parameters for "pref_tx_ring_sz"
> > and "pref_rx_ring_sz" too. While it is the case that, once the structure
> > is changed, we can make multiple additional changes, I think it might be
> > worth mentioning as many as we can for completeness.
> > 
> > Another point to consider, is whether we might want to add in a
> > sub-structure for "preferred_settings" to hold all these, rather than
> > just adding them as new fields. It might help with making names more
> > readable (though also longer).
> > 
> > 	struct {
> > 		uint16_t rx_burst;
> > 		uint16_t tx_burst;
> > 		uint16_t rx_ring_sz;
> > 		uint16_t tx_ring_sz;
> > 	} preferred_settings;
> 
> This, and the point above that we can make multiple additional changes, is
> definitely a good idea. Though, 'preferred_setting' is long and has chances
> of spell mistakes in first go - what about just 'pref' or, 'pref_size' if
> only 4 mentioned above are part of this.
> 
> For now I saw need for burst size because I hit that case. Ring size looks
> logical to me. We can have a look if more such toggles are required.
> 

I actually don't like the abbreviation "pref", as it looks too much like
"perf" short for performance. As this is an initialization setting, I
also don't think having a longer name is that big of deal. How about
calling them "suggested" or "recommended" settings - both of which have
less fiddly spellings.

/Bruce