Re: [dpdk-dev] [PATCH v3 1/3] rte_ethdev: Add API function to read dev clock

["Wiles, Keith" <keith.wiles@intel.com>]

> On Apr 24, 2019, at 12:34 PM, Tom Barbette <barbette@kth.se> wrote:
> 
> Add rte_eth_read_clock to read the raw clock of a devide.
> 
> The main use is to get the device clock conversion co-efficients to be
> able to translate the raw clock of the timestamp field of the pkt mbuf
> to a local synced time value.
> 
> This function was missing to allow users to convert the RX timestamp field
> to real time without the complexity of the rte_timesync* facility. One can
> derivate the clock frequency by calling twice read_clock and then keep a
> common time base.
> 
> Signed-off-by: Tom Barbette <barbette@kth.se>
> ---
> doc/guides/nics/features.rst             |  1 +
> lib/librte_ethdev/rte_ethdev.c           | 13 +++++++
> lib/librte_ethdev/rte_ethdev.h           | 45 ++++++++++++++++++++++++
> lib/librte_ethdev/rte_ethdev_core.h      |  6 ++++
> lib/librte_ethdev/rte_ethdev_version.map |  2 ++
> lib/librte_mbuf/rte_mbuf.h               |  2 ++
> 6 files changed, 69 insertions(+)
> 
> diff --git a/doc/guides/nics/features.rst b/doc/guides/nics/features.rst
> index c5bf32222..025b7f812 100644
> --- a/doc/guides/nics/features.rst
> +++ b/doc/guides/nics/features.rst
> @@ -602,6 +602,7 @@ Supports Timestamp.
> * **[provides] mbuf**: ``mbuf.ol_flags:PKT_RX_TIMESTAMP``.
> * **[provides] mbuf**: ``mbuf.timestamp``.
> * **[provides] rte_eth_dev_info**: ``rx_offload_capa,rx_queue_offload_capa: DEV_RX_OFFLOAD_TIMESTAMP``.
> +* **[related] eth_dev_ops**: ``read_clock``.
> 
> .. _nic_features_macsec_offload:
> 
> diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
> index d7cfa3d53..22e35d839 100644
> --- a/lib/librte_ethdev/rte_ethdev.c
> +++ b/lib/librte_ethdev/rte_ethdev.c
> @@ -4170,6 +4170,19 @@ rte_eth_timesync_write_time(uint16_t port_id, const struct timespec *timestamp)
> 								timestamp));
> }
> 
> +int
> +rte_eth_read_clock(uint16_t port_id, uint64_t *timestamp)
> +{
> +	struct rte_eth_dev *dev;
> +
> +	RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -ENODEV);
> +	dev = &rte_eth_devices[port_id];
> +
> +	RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->read_clock, -ENOTSUP);
> +	return eth_err(port_id, (*dev->dev_ops->read_clock)(dev,
> +								timestamp));
> +}
> +
> int
> rte_eth_dev_get_reg_info(uint16_t port_id, struct rte_dev_reg_info *info)
> {
> diff --git a/lib/librte_ethdev/rte_ethdev.h b/lib/librte_ethdev/rte_ethdev.h
> index b8d19c69f..dfaf16a56 100644
> --- a/lib/librte_ethdev/rte_ethdev.h
> +++ b/lib/librte_ethdev/rte_ethdev.h
> @@ -3793,6 +3793,51 @@ int rte_eth_timesync_read_time(uint16_t port_id, struct timespec *time);
>  */
> int rte_eth_timesync_write_time(uint16_t port_id, const struct timespec *time);
> 
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Read the current clock counter of an Ethernet device
> + *
> + * This returns the current raw clock value of an Ethernet device.
> + * The value returned here is from the same clock than the one
> + * filling timestamp field of RX packets. Therefore it can be used
> + * to compute a precise conversion of the device clock to the real time.
> + *
> + * E.g, a simple heuristic to derivate the frequency would be:
> + * uint64_t start, end;
> + * rte_eth_read_clock(port, start);
> + * rte_delay_ms(100);
> + * rte_eth_read_clock(port, end);
> + * double freq = (end - start) * 10;
> + *
> + * Compute a common reference with:
> + * uint64_t base_time_sec = current_time();
> + * uint64_t base_clock;
> + * rte_eth_read_clock(port, base_clock);
> + *
> + * Then, convert the raw mbuf timestamp with:
> + * base_time_sec + (double)(mbuf->timestamp - base_clock) / freq;
> + *
> + * This simple example will not provide a very good accuracy. One must
> + * at least measure multiple times the frequency and do a regression.
> + * To avoid deviation from the system time, the common reference can
> + * be repeated from time to time. The integer division can also be
> + * converted by a multiplication and a shift for better performance.
> + *
> + * @param port_id
> + *   The port identifier of the Ethernet device.
> + * @param time
> + *   Pointer to the uint64_t that holds the raw clock value.

What is a raw clock value? It took me a bit to find that it is in nano-seconds need to document that point.
> + *
> + * @return
> + *   - 0: Success.
> + *   - -ENODEV: The port ID is invalid.
> + *   - -ENOTSUP: The function is not supported by the Ethernet driver.
> + */
> +int __rte_experimental
> +rte_eth_read_clock(uint16_t port_id, uint64_t *timestamp);

Using timestamp variable is not very descriptive and some other name needs to be used. Also in the driver it is called *clock.

Another question is why does this routine not perform the looping/delaying and calling read_clock and then return frequency instead. If you want a timestamp reading function then this one is not being described that way and I would think it should be done someplace else or should be.
> +
> /**
>  * Config l2 tunnel ether type of an Ethernet device for filtering specific
>  * tunnel packets by ether type.
> diff --git a/lib/librte_ethdev/rte_ethdev_core.h b/lib/librte_ethdev/rte_ethdev_core.h
> index 8f03f83f6..86806b3eb 100644
> --- a/lib/librte_ethdev/rte_ethdev_core.h
> +++ b/lib/librte_ethdev/rte_ethdev_core.h
> @@ -322,6 +322,10 @@ typedef int (*eth_timesync_write_time)(struct rte_eth_dev *dev,
> 				       const struct timespec *timestamp);
> /**< @internal Function used to get time from the device clock */
> 
> +typedef int (*eth_read_clock)(struct rte_eth_dev *dev,
> +				      uint64_t *timestamp);
> +/**< @internal Function used to get the current value of the device clock. */
> +
> typedef int (*eth_get_reg_t)(struct rte_eth_dev *dev,
> 				struct rte_dev_reg_info *info);
> /**< @internal Retrieve registers  */
> @@ -496,6 +500,8 @@ struct eth_dev_ops {
> 	eth_timesync_read_time     timesync_read_time; /** Get the device clock time. */
> 	eth_timesync_write_time    timesync_write_time; /** Set the device clock time. */
> 
> +	eth_read_clock             read_clock;
> +
> 	eth_xstats_get_by_id_t     xstats_get_by_id;
> 	/**< Get extended device statistic values by ID. */
> 	eth_xstats_get_names_by_id_t xstats_get_names_by_id;
> diff --git a/lib/librte_ethdev/rte_ethdev_version.map b/lib/librte_ethdev/rte_ethdev_version.map
> index afcd25599..670e4fad5 100644
> --- a/lib/librte_ethdev/rte_ethdev_version.map
> +++ b/lib/librte_ethdev/rte_ethdev_version.map
> @@ -253,10 +253,12 @@ EXPERIMENTAL {
> 	rte_eth_dev_rx_intr_ctl_q_get_fd;
> 	rte_eth_find_next_of;
> 	rte_eth_find_next_sibling;
> +	rte_eth_read_clock;
> 	rte_eth_switch_domain_alloc;
> 	rte_eth_switch_domain_free;
> 	rte_flow_conv;
> 	rte_flow_expand_rss;
> +	rte_eth_read_clock;
> 	rte_mtr_capabilities_get;
> 	rte_mtr_create;
> 	rte_mtr_destroy;
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index 68415af02..e530a96c5 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -668,6 +668,8 @@ struct rte_mbuf {
> 
> 	/** Valid if PKT_RX_TIMESTAMP is set. The unit and time reference
> 	 * are not normalized but are always the same for a given port.
> +	 * Some devices allow to query rte_eth_read_clock that will return the
> +	 * current device timestamp.

The message here is not a good place for this detail, I would put it in the function call doc above.
> 	 */
> 	uint64_t timestamp;
> 
> -- 
> 2.17.1
> 

Regards,
Keith