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From: Stephen Hemminger <stephen@networkplumber.org>
To: Tom Barbette <barbette@kth.se>
Cc: dev@dpdk.org, bruce.richardson@intel.com,
	john.mcnamara@intel.com, Thomas Monjalon <thomas@monjalon.net>,
	Ferruh Yigit <ferruh.yigit@intel.com>,
	Andrew Rybchenko <arybchenko@solarflare.com>,
	Shahaf Shuler <shahafs@mellanox.com>,
	Yongseok Koh <yskoh@mellanox.com>
Subject: Re: [dpdk-dev] [PATCH v2 0/3] Add rte_eth_read_clock API
Date: Wed, 27 Mar 2019 07:41:12 -0700	[thread overview]
Message-ID: <20190327074112.427c4758@shemminger-XPS-13-9360> (raw)
In-Reply-To: <20190327061935.19572-1-barbette@kth.se>

On Wed, 27 Mar 2019 07:19:32 +0100
Tom Barbette <barbette@kth.se> wrote:

> Some NICs allow to timestamp packets, but do not support the full
> PTP synchronization process. Hence, the value set in the mbuf
> timestamp field is only the raw value of an internal clock.
> 
> To make sense of this value, one at least needs to be able to query
> the current hardware clock value. As with the TSC, from there
> a frequency can be derieved by querying multiple time the current value of the
> internal clock with some known delay between the queries (example
> provided in the API doc).
> 
> This patch series adds support for MLX5.
> 
> An example app is provided in the rxtx_callback application.
> It has been updated to display, on top of the software latency
> in cycles, the total latency since the packet was received in hardware.
> The API is used to compute a delta in the TX callback. The raw amount of
> ticks is converted to cycles using a variation of the technique describe above.
> 
> Aside from offloading timestamping, which relieve the
> software from a few operations, this allows to get much more precision
> when studying the source of the latency in a system.
> Eg. in our 100G, CX5 setup the rxtx callback application shows
> SW latency is around 74 cycles (TSC is 3.2Ghz), but the latency
> including NIC processing, PCIe, and queuing is around 196 cycles.
> 
> One may think at first this API is overlapping with te_eth_timesync_read_time.
> rte_eth_timesync_read_time is clearly identified as part of a set of functions
> to use PTP synchronization.
> The device raw clock is not "sync" in any way. More importantly, the returned
> value is not a timeval, but an amount of ticks. We could have a cast-based
> solution, but on top of being an ugly solution, some people seeing the timeval
> type of rte_eth_timesync_read_time could use it blindly.
> 
> Change in v2:
>   - Rebase on current master
> 
> Tom Barbette (3):
>   rte_ethdev: Add API function to read dev clock
>   mlx5: Implement support for read_clock
>   rxtx_callbacks: Add support for HW timestamp
> 
>  doc/guides/nics/features.rst                |  1 +
>  doc/guides/sample_app_ug/rxtx_callbacks.rst |  9 ++-
>  drivers/net/mlx5/mlx5.c                     |  1 +
>  drivers/net/mlx5/mlx5.h                     |  1 +
>  drivers/net/mlx5/mlx5_ethdev.c              | 29 +++++++
>  drivers/net/mlx5/mlx5_glue.c                |  8 ++
>  drivers/net/mlx5/mlx5_glue.h                |  2 +
>  examples/rxtx_callbacks/Makefile            |  2 +
>  examples/rxtx_callbacks/main.c              | 86 ++++++++++++++++++++-
>  examples/rxtx_callbacks/meson.build         |  1 +
>  lib/librte_ethdev/rte_ethdev.c              | 13 ++++
>  lib/librte_ethdev/rte_ethdev.h              | 44 +++++++++++
>  lib/librte_ethdev/rte_ethdev_core.h         |  6 ++
>  lib/librte_ethdev/rte_ethdev_version.map    |  1 +
>  lib/librte_mbuf/rte_mbuf.h                  |  2 +
>  15 files changed, 201 insertions(+), 5 deletions(-)


I like this approach but would like to see the same API supported
on multiple devices.

The current timestamp API is a mess because not all devices behave the
same way. Trying to write an application that uses timestamping is therefore
very difficult.

  parent reply	other threads:[~2019-03-27 14:41 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-27  6:19 Tom Barbette
2019-03-27  6:19 ` Tom Barbette
2019-03-27  6:19 ` [dpdk-dev] [PATCH v2 1/3] rte_ethdev: Add API function to read dev clock Tom Barbette
2019-03-27  6:19   ` Tom Barbette
2019-04-02 17:46   ` Ferruh Yigit
2019-04-02 17:46     ` Ferruh Yigit
2019-04-02 19:24     ` Tom Barbette
2019-04-02 19:24       ` Tom Barbette
2019-03-27  6:19 ` [dpdk-dev] [PATCH v2 2/3] mlx5: Implement support for read_clock Tom Barbette
2019-03-27  6:19   ` Tom Barbette
2019-04-02 17:47   ` Ferruh Yigit
2019-04-02 17:47     ` Ferruh Yigit
2019-04-02 18:26   ` Ferruh Yigit
2019-04-02 18:26     ` Ferruh Yigit
2019-04-02 19:05     ` Tom Barbette
2019-04-02 19:05       ` Tom Barbette
2019-04-03  5:28   ` Shahaf Shuler
2019-04-03  5:28     ` Shahaf Shuler
2019-03-27  6:19 ` [dpdk-dev] [PATCH v2 3/3] rxtx_callbacks: Add support for HW timestamp Tom Barbette
2019-03-27  6:19   ` Tom Barbette
2019-04-02 18:22   ` Ferruh Yigit
2019-04-02 18:22     ` Ferruh Yigit
2019-04-02 19:39     ` Tom Barbette
2019-04-02 19:39       ` Tom Barbette
2019-03-27 14:41 ` Stephen Hemminger [this message]
2019-03-27 14:41   ` [dpdk-dev] [PATCH v2 0/3] Add rte_eth_read_clock API Stephen Hemminger
2019-03-27 14:48   ` Thomas Monjalon
2019-03-27 14:48     ` Thomas Monjalon
2019-03-27 14:54   ` Wiles, Keith
2019-03-27 14:54     ` Wiles, Keith
2019-03-27 16:08     ` Tom Barbette
2019-03-27 16:08       ` Tom Barbette

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