Re: [dpdk-dev] [PATCH v3 2/2] net/failsafe: add timestamp to stats snapshot

["Gaëtan Rivet" <gaetan.rivet@6wind.com>]

On Sat, Oct 21, 2017 at 08:54:46PM +0000, Matan Azrad wrote:
> Fail-safe attempts to read an ultimate statistics on removal time; if
> that fails, it uses the latest recorded snapshot.
> 
> This patch adds timestamp for each stats snapshot to allow a time report
> since the last snapshot in case of the above failure.
> 
> By this way, the user can estimate the stats read accuracy.
> 
> Signed-off-by: Matan Azrad <matan@mellanox.com>
Acked-by: Gaetan Rivet <gaetan.rivet@6wind.com>
> ---
>  drivers/net/failsafe/failsafe_ether.c   | 17 ++++++++++++-----
>  drivers/net/failsafe/failsafe_ops.c     | 10 ++++++++--
>  drivers/net/failsafe/failsafe_private.h |  7 ++++++-
>  3 files changed, 26 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/failsafe/failsafe_ether.c b/drivers/net/failsafe/failsafe_ether.c
> index 0282891..6cb435f 100644
> --- a/drivers/net/failsafe/failsafe_ether.c
> +++ b/drivers/net/failsafe/failsafe_ether.c
> @@ -35,6 +35,7 @@
>  
>  #include <rte_flow.h>
>  #include <rte_flow_driver.h>
> +#include <rte_cycles.h>
>  
>  #include "failsafe_private.h"
>  
> @@ -317,12 +318,18 @@
>  
>  	/* Attempt to read current stats. */
>  	err = rte_eth_stats_get(PORT_ID(sdev), &stats);
> -	if (err)
> -		WARN("Could not access latest statistics from sub-device %d,"
> -			 " using latest snapshot.\n", SUB_ID(sdev));
> +	if (err) {
> +		uint64_t timestamp = sdev->stats_snapshot.timestamp;
> +
> +		WARN("Could not access latest statistics from sub-device %d.\n",
> +			 SUB_ID(sdev));
> +		if (timestamp != 0)
> +			WARN("Using latest snapshot taken before %lu seconds.\n",
> +				 (rte_rdtsc() - timestamp) / rte_get_tsc_hz());
> +	}
>  	failsafe_stats_increment(&PRIV(sdev->fs_dev)->stats_accumulator,
> -			err ? &sdev->stats_snapshot : &stats);
> -	memset(&sdev->stats_snapshot, 0, sizeof(struct rte_eth_stats));
> +			err ? &sdev->stats_snapshot.stats : &stats);
> +	memset(&sdev->stats_snapshot, 0, sizeof(sdev->stats_snapshot));
>  }
>  
>  static inline int
> diff --git a/drivers/net/failsafe/failsafe_ops.c b/drivers/net/failsafe/failsafe_ops.c
> index d360965..f460551 100644
> --- a/drivers/net/failsafe/failsafe_ops.c
> +++ b/drivers/net/failsafe/failsafe_ops.c
> @@ -38,6 +38,7 @@
>  #include <rte_ethdev.h>
>  #include <rte_malloc.h>
>  #include <rte_flow.h>
> +#include <rte_cycles.h>
>  
>  #include "failsafe_private.h"
>  
> @@ -592,13 +593,18 @@
>  
>  	rte_memcpy(stats, &PRIV(dev)->stats_accumulator, sizeof(*stats));
>  	FOREACH_SUBDEV_STATE(sdev, i, dev, DEV_ACTIVE) {
> -		ret = rte_eth_stats_get(PORT_ID(sdev), &sdev->stats_snapshot);
> +		struct rte_eth_stats *snapshot = &sdev->stats_snapshot.stats;
> +		uint64_t *timestamp = &sdev->stats_snapshot.timestamp;
> +
> +		ret = rte_eth_stats_get(PORT_ID(sdev), snapshot);
>  		if (ret) {
>  			ERROR("Operation rte_eth_stats_get failed for sub_device %d with error %d",
>  				  i, ret);
> +			*timestamp = 0;
>  			return ret;
>  		}
> -		failsafe_stats_increment(stats, &sdev->stats_snapshot);
> +		*timestamp = rte_rdtsc();
> +		failsafe_stats_increment(stats, snapshot);
>  	}
>  	return 0;
>  }
> diff --git a/drivers/net/failsafe/failsafe_private.h b/drivers/net/failsafe/failsafe_private.h
> index d343ebf..d81cc3c 100644
> --- a/drivers/net/failsafe/failsafe_private.h
> +++ b/drivers/net/failsafe/failsafe_private.h
> @@ -93,6 +93,11 @@ enum dev_state {
>  	DEV_STARTED,
>  };
>  
> +struct fs_stats {
> +	struct rte_eth_stats stats;
> +	uint64_t timestamp;
> +};
> +
>  struct sub_device {
>  	/* Exhaustive DPDK device description */
>  	struct rte_devargs devargs;
> @@ -103,7 +108,7 @@ struct sub_device {
>  	/* Device state machine */
>  	enum dev_state state;
>  	/* Last stats snapshot passed to user */
> -	struct rte_eth_stats stats_snapshot;
> +	struct fs_stats stats_snapshot;
>  	/* Some device are defined as a command line */
>  	char *cmdline;
>  	/* fail-safe device backreference */
> -- 
> 1.8.3.1
> 

-- 
Gaëtan Rivet
6WIND