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

[Andrew Rybchenko <arybchenko@solarflare.com>]

On 4/24/19 8:34 PM, Tom Barbette wrote:
> Add rte_eth_read_clock to read the raw clock of a devide.

Typo above "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

RX -> Rx

> 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>

[snip]

> 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));

Why timestamp on the next line?

> +}
> +
>   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

RX -> Rx

> + * 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.
> + *
> + * @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);
> +
>   /**
>    * Config l2 tunnel ether type of an Ethernet device for filtering specific
>    * tunnel packets by ether type.

[snip]

> 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;

Dup

[snip]