From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ferruh Yigit <ferruh.yigit@intel.com>
Subject: Re: [PATCH 1/3] rte_ethdev: Add API function to read dev
	clock
Date: Thu, 20 Dec 2018 19:55:11 +0000
Message-ID: <491a4e29-83dd-ad0c-8904-d1e2ccca1f68@intel.com>
References: <20181219134934.24693-1-barbette@kth.se>
 <20181219134934.24693-2-barbette@kth.se>
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Cc: bruce.richardson@intel.com, john.mcnamara@intel.com,
 Thomas Monjalon <thomas@monjalon.net>,
 Andrew Rybchenko <arybchenko@solarflare.com>,
 Shahaf Shuler <shahafs@mellanox.com>, Yongseok Koh <yskoh@mellanox.com>
To: Tom Barbette <barbette@kth.se>, dev@dpdk.org
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On 12/19/2018 1:49 PM, Tom Barbette wrote:
> +/**
> + * @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.
> + *
> + * @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 *time);

Is this a common enough feature to include into ethdev abstraction layer? Or a
feature for a single vendor?
I would like to get more input from other vendors if this is something they can
benefit from?