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

[Olivier Matz <olivier.matz@6wind.com>]

Hi,

On Mon, Oct 05, 2020 at 01:23:08PM +0100, Ferruh Yigit wrote:
> On 9/28/2020 4:43 PM, Stephen Hemminger wrote:
> > On Mon, 28 Sep 2020 17:24:26 +0200
> > Thomas Monjalon <thomas@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@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"
> > 
> 
> The current issue is not directly related to '*_queue_stats_mapping' APIs.
> 
> Problem is not able to set 'RTE_ETHDEV_QUEUE_STAT_CNTRS' > 255.
> User may need to set the 'RTE_ETHDEV_QUEUE_STAT_CNTRS' > 255, since it is
> used to define size of the stats counter.
> "uint64_t q_ipackets[RTE_ETHDEV_QUEUE_STAT_CNTRS];"
> 
> When 'RTE_ETHDEV_QUEUE_STAT_CNTRS' > 255, it gives multiple build errors,
> the one in the ethdev is like [1].
> 
> This can be fixed two ways,
> a) increase the size of 'stat_idx' storage type to u16 in the
> '*_queue_stats_mapping' APIs, this is what this patch does.
> b) Fix with a casting in the comparison, without changing the APIs.
> 
> I think both are OK, but is (b) more preferable?

I think the patch (a) is ok, knowing that RTE_ETHDEV_QUEUE_STAT_CNTRS is
not modified.

On the substance, I agree with Thomas that the queue_stats_mapping API
should be replaced by xstats.


> 
> 
> [1]
> ../lib/librte_ethdev/rte_ethdev.c: In function ‘set_queue_stats_mapping’:
> ../lib/librte_ethdev/rte_ethdev.c:2943:15: warning: comparison is always
> false due to limited range of data type [-Wtype-limits]
>  2943 |  if (stat_idx >= RTE_ETHDEV_QUEUE_STAT_CNTRS)
>       |               ^~