Re: [dpdk-dev] [PATCH v7 1/2] mbuf: introduce accurate packet Tx scheduling

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 7/10/2020 4:46 PM, Slava Ovsiienko wrote:
> 
> 
>> -----Original Message-----
>> From: dev <dev-bounces@dpdk.org> On Behalf Of Viacheslav Ovsiienko
>> Sent: Friday, July 10, 2020 15:40
>> To: dev@dpdk.org
>> Cc: Matan Azrad <matan@mellanox.com>; Raslan Darawsheh
>> <rasland@mellanox.com>; olivier.matz@6wind.com;
>> arybchenko@solarflare.com; Thomas Monjalon <thomas@monjalon.net>;
>> ferruh.yigit@intel.com
>> Subject: [dpdk-dev] [PATCH v7 1/2] mbuf: introduce accurate packet Tx
>> scheduling
>>
>> There is the requirement on some networks for precise traffic timing
>> management. The ability to send (and, generally speaking, receive) the
>> packets at the very precisely specified moment of time provides the
>> opportunity to support the connections with Time Division Multiplexing using
>> the contemporary general purpose NIC without involving an auxiliary
>> hardware. For example, the supporting of O-RAN Fronthaul interface is one
>> of the promising features for potentially usage of the precise time
>> management for the egress packets.
>>
>> The main objective of this patchset is to specify the way how applications
>> can provide the moment of time at what the packet transmission must be
>> started and to describe in preliminary the supporting this feature from mlx5
>> PMD side [1].
>>
>> The new dynamic timestamp field is proposed, it provides some timing
>> information, the units and time references (initial phase) are not explicitly
>> defined but are maintained always the same for a given port.
>> Some devices allow to query rte_eth_read_clock() that will return the current
>> device timestamp. The dynamic timestamp flag tells whether the field
>> contains actual timestamp value. For the packets being sent this value can be
>> used by PMD to schedule packet sending.
>>
>> The device clock is opaque entity, the units and frequency are vendor specific
>> and might depend on hardware capabilities and configurations. If might (or
>> not) be synchronized with real time via PTP, might (or not) be synchronous
>> with CPU clock (for example if NIC and CPU share the same clock source
>> there might be no any drift between the NIC and CPU clocks), etc.
>>
>> After PKT_RX_TIMESTAMP flag and fixed timestamp field supposed
>> deprecation and obsoleting, these dynamic flag and field might be used to
>> manage the timestamps on receiving datapath as well. Having the dedicated
>> flags for Rx/Tx timestamps allows applications not to perform explicit flags
>> reset on forwarding and not to promote received timestamps to the
>> transmitting datapath by default.
>> The static PKT_RX_TIMESTAMP is considered as candidate to become the
>> dynamic flag and this move should be discussed.
>>
>> When PMD sees the "rte_dynfield_timestamp" set on the packet being sent it
>> tries to synchronize the time of packet appearing on the wire with the
>> specified packet timestamp. If the specified one is in the past it should be
>> ignored, if one is in the distant future it should be capped with some
>> reasonable value (in range of seconds). These specific cases ("too late" and
>> "distant future") can be optionally reported via device xstats to assist
>> applications to detect the time-related problems.
>>
>> There is no any packet reordering according timestamps is supposed, neither
>> within packet burst, nor between packets, it is an entirely application
>> responsibility to generate packets and its timestamps in desired order. The
>> timestamps can be put only in the first packet in the burst providing the
>> entire burst scheduling.
>>
>> PMD reports the ability to synchronize packet sending on timestamp with
>> new offload flag:
>>
>> This is palliative and might be replaced with new eth_dev API about
>> reporting/managing the supported dynamic flags and its related features.
>> This API would break ABI compatibility and can't be introduced at the
>> moment, so is postponed to 20.11.
>>
>> For testing purposes it is proposed to update testpmd "txonly"
>> forwarding mode routine. With this update testpmd application generates
>> the packets and sets the dynamic timestamps according to specified time
>> pattern if it sees the "rte_dynfield_timestamp" is registered.
>>
>> The new testpmd command is proposed to configure sending pattern:
>>
>> set tx_times <burst_gap>,<intra_gap>
>>
>> <intra_gap> - the delay between the packets within the burst
>>               specified in the device clock units. The number
>>               of packets in the burst is defined by txburst parameter
>>
>> <burst_gap> - the delay between the bursts in the device clock units
>>
>> As the result the bursts of packet will be transmitted with specific delays
>> between the packets within the burst and specific delay between the bursts.
>> The rte_eth_read_clock is supposed to be engaged to get the current device
>> clock value and provide the reference for the timestamps.
>>
>> [1]
>> https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fpatche
>> s.dpdk.org%2Fpatch%2F73714%2F&amp;data=02%7C01%7Cviacheslavo%40
>> mellanox.com%7C810609c61c3b466e8f5a08d824ce57f8%7Ca652971c7d2e4
>> d9ba6a4d149256f461b%7C0%7C0%7C637299815958194092&amp;sdata=H
>> D7efBGOLuYxHd5KLJYJj7RSbiLRVBNm5jdq%2FJv%2FXfk%3D&amp;reserved=
>> 0
>>
>> Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
> 
>  promote Acked-bt from previous patch version to maintain patchwork 
>  status accordingly
> 
> Acked-by: Olivier Matz <olivier.matz@6wind.com>
> 

For series,
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>

Applied to dpdk-next-net/master, thanks.