[dpdk-dev] [dpdk-techboard] [PATCH V5 1/2] dpdk: resolve compiling errors for per-queue stats

[Stephen Hemminger]

On Mon, 28 Sep 2020 17:24:26 +0200
Thomas Monjalon <thomas at monjalon.net> wrote:

> 28/09/2020 15:53, Ferruh Yigit:
> > On 9/28/2020 10:16 AM, Thomas Monjalon wrote:  
> > > 28/09/2020 10:59, Ferruh Yigit:  
> > >> On 9/27/2020 4:16 AM, Min Hu (Connor) wrote:  
> > >>> From: Huisong Li <lihuisong at huawei.com>
> > >>>
> > >>> Currently, only statistics of rx/tx queues with queue_id less than
> > >>> RTE_ETHDEV_QUEUE_STAT_CNTRS can be displayed. If there is a certain
> > >>> application scenario that it needs to use 256 or more than 256 queues
> > >>> and display all statistics of rx/tx queue. At this moment, we have to
> > >>> change the macro to be equaled to the queue number.
> > >>>
> > >>> However, modifying the macro to be greater than 256 will trigger
> > >>> many errors and warnings from test-pmd, PMD drivers and librte_ethdev
> > >>> during compiling dpdk project. But it is possible and permitted that
> > >>> rx/tx queue number is greater than 256 and all statistics of rx/tx
> > >>> queue need to be displayed. In addition, the data type of rx/tx queue
> > >>> number in rte_eth_dev_configure API is 'uint16_t'. So It is unreasonable
> > >>> to use the 'uint8_t' type for variables that control which per-queue
> > >>> statistics can be displayed.  
> > > 
> > > The explanation is too much complex and misleading.
> > > You mean you cannot increase RTE_ETHDEV_QUEUE_STAT_CNTRS
> > > above 256 because it is an 8-bit type?
> > > 
> > > [...]  
> > >>> --- a/lib/librte_ethdev/rte_ethdev.h
> > >>> +++ b/lib/librte_ethdev/rte_ethdev.h
> > >>>    int rte_eth_dev_set_tx_queue_stats_mapping(uint16_t port_id,
> > >>> -		uint16_t tx_queue_id, uint8_t stat_idx);
> > >>> +		uint16_t tx_queue_id, uint16_t stat_idx);  
> > > [...]  
> > >>>    int rte_eth_dev_set_rx_queue_stats_mapping(uint16_t port_id,
> > >>>    					   uint16_t rx_queue_id,
> > >>> -					   uint8_t stat_idx);
> > >>> +					   uint16_t stat_idx);  
> > > [...]  
> > >> cc'ed tech-board,
> > >>
> > >> The patch breaks the ethdev ABI without a deprecation notice from previous
> > >> release(s).
> > >>
> > >> It is mainly a fix to the port_id storage type, which we have updated from
> > >> uint8_t to uint16_t in past but some seems remained for
> > >> 'rte_eth_dev_set_tx_queue_stats_mapping()' &
> > >> 'rte_eth_dev_set_rx_queue_stats_mapping()' APIs.  
> > > 
> > > No, it is not related to the port id, but the number of limited stats.
> > >   
> > 
> > Right, it is not related to the port id, it is fixing the storage type for index 
> > used to map the queue stats.
> >   
> > >> Since the ethdev library already heavily breaks the ABI this release, I am for
> > >> getting this fix, instead of waiting the fix for one more year.  
> > > 
> > > If stats can be managed for more than 256 queues, I think it means
> > > it is not limited. In this case, we probably don't need the API
> > > *_queue_stats_mapping which was invented for a limitation of ixgbe.
> > > 
> > > The problem is probably somewhere else (in testpmd),
> > > that's why I am against this patch.
> > >   
> > 
> > This patch is not to fix queue stats mapping, I agree there are problems related 
> > to it, already shared as comment to this set.
> > 
> > But this patch is to fix the build errors when 'RTE_ETHDEV_QUEUE_STAT_CNTRS' 
> > needs to set more than 255. Where the build errors seems around the 
> > stats_mapping APIs.  
> 
> It is not said this API is supposed to manage more than 256 queues mapping.
> In general we should not need this API.
> I think it is solving the wrong problem.


The original API is a band aid for the limited number of statistics counters
in the Intel IXGBE hardware. It crept into to the DPDK as an API. I would rather
have per-queue statistics and make ixgbe say "not supported"