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

[Shreyansh Jain <shreyansh.jain@nxp.com>]

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.

> 
> In any case, for this or subsequent versions:
> 
> Acked-by: Bruce Richardson <bruce.richardson@intel.com>
> 
> /Bruce
> 

Thanks.