Re: [dpdk-dev] [PATCH] app/testpmd: fix statistics in multiple process

["Li, Xiaoyun" <xiaoyun.li@intel.com>]

Hi

> -----Original Message-----
> From: Min Hu (Connor) <humin29@huawei.com>
> Sent: Tuesday, September 14, 2021 11:13
> To: dev@dpdk.org
> Cc: Yigit, Ferruh <ferruh.yigit@intel.com>; Li, Xiaoyun <xiaoyun.li@intel.com>
> Subject: [PATCH] app/testpmd: fix statistics in multiple process
> 
> Currently, 'clear port stats all' in secondary will clear stats in PMD, and also
> update stats which APP stores in 'ports[]' array in secondary process, note that,
> that in primary process remains unchanged. So, when 'show fwd stats all' in
> primary process, stats in PMD may be less than stats which APP stores in 'ports[]'
> array(the stats is different with that in secondary). So forward statistics(stats in
> PMD minus stats which APP stores in 'ports[]' array) will be wrong. Like this:
> ---------------------- Forward statistics for port 0  --------------
> RX-packets: 18446744073703120168 RX-dropped: 18446744073704076766
> RX-total: 18446744073697645318
> TX-packets: 18446744073703122216 TX-dropped: 0
> TX-total: 18446744073703122216
> --------------------------------------------------------------------
> Stats in PMD are shared between multiple processes, but stats which APP stores
> have their own copies in multiple processes. And this will result in bugs.
> 
> This patch will fix it by creating shared memory to store last stats for multiple
> and secondary process in testpmd.

Why not just limit "clear port stats " behavior to only primary process?
Is there any particular reason second process has to do clear stats?

Stats is quite complicate struct. I feel like it will have race condition issue if you allow two processes to clear it.
Only allow getting for multiple processes makes more sense.

Also your patch has issues even if this idea is accepted by others. Please see below.

> 
> Fixes: 184de26c78d0 ("app/testpmd: support multi-process")
> 
> Signed-off-by: Min Hu (Connor) <humin29@huawei.com>
> ---
>  app/test-pmd/config.c  |  4 +--
>  app/test-pmd/testpmd.c | 63 ++++++++++++++++++++++++++++++++++++------
>  app/test-pmd/testpmd.h |  2 +-
>  3 files changed, 58 insertions(+), 11 deletions(-)
> 
<snip>
> @@ -3572,6 +3614,7 @@ init_port_config(void)
>  			port->dev_conf.intr_conf.lsc = 1;
>  		if (rmv_interrupt && (*port->dev_info.dev_flags &
> RTE_ETH_DEV_INTR_RMV))
>  			port->dev_conf.intr_conf.rmv = 1;
> +		port_stats_init(pid);

Init_port_config is called in several places. Why init stats as 0 for port->stats here?
You did so. Then if user use cmd like "port config 0 rxq 2" which calls init_port_config, port->stats is cleared while device stats isn't.
Then the fwd stats you got will be wrong.

Please read code carefully. Port->stats will be reset as device stats when start_fwd. Not reset as 0.

Port->stats should be only cleared when you do clear_nic_stats. Otherwise, it doesn't make sense as "last port stats".

>  	}
>  }
> 
> @@ -3882,6 +3925,10 @@ main(int argc, char** argv)
>  		rte_exit(EXIT_FAILURE, "Cannot init EAL: %s\n",
>  			 rte_strerror(rte_errno));
> 
> +	ret = eth_stats_zone_reserve();
> +	if (ret != 0)
> +		rte_exit(EXIT_FAILURE, "Allocate memzone ethdev stats failed");
> +
>  	ret = register_eth_event_callback();
>  	if (ret != 0)
>  		rte_exit(EXIT_FAILURE, "Cannot register for ethdev events");
> diff --git a/app/test-pmd/testpmd.h b/app/test-pmd/testpmd.h index
> 5863b2f43f..a48a302343 100644
> --- a/app/test-pmd/testpmd.h
> +++ b/app/test-pmd/testpmd.h
> @@ -202,7 +202,7 @@ struct rte_port {
>  	struct rte_eth_dev_info dev_info;   /**< PCI info + driver name */
>  	struct rte_eth_conf     dev_conf;   /**< Port configuration. */
>  	struct rte_ether_addr       eth_addr;   /**< Port ethernet address */
> -	struct rte_eth_stats    stats;      /**< Last port statistics */
> +	struct rte_eth_stats    *stats;      /**< Last port statistics */
>  	unsigned int            socket_id;  /**< For NUMA support */
>  	uint16_t		parse_tunnel:1; /**< Parse internal headers */
>  	uint16_t                tso_segsz;  /**< Segmentation offload MSS for non-
> tunneled packets. */
> --
> 2.33.0