Re: [dpdk-dev] [PATCH v5 1/2] mbuf: introduce accurate packet Tx scheduling

[Slava Ovsiienko <viacheslavo@mellanox.com>]

> promote Acked-bt from previous patch version to maintain patchwork status accordingly

Acked-by: Olivier Matz <olivier.matz@6wind.com>

> -----Original Message-----
> From: dev <dev-bounces@dpdk.org> On Behalf Of Viacheslav Ovsiienko
> Sent: Wednesday, July 8, 2020 18:47
> To: dev@dpdk.org
> Cc: Matan Azrad <matan@mellanox.com>; Raslan Darawsheh
> <rasland@mellanox.com>; olivier.matz@6wind.com;
> bernard.iremonger@intel.com; thomas@monjalon.com;
> mb@smartsharesystems.com
> Subject: [dpdk-dev] [PATCH v5 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 RFC 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.
> 
> 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 deprecation and
> obsoleting, these dynamic flag and field will 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.
> 
> 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 is going to 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_get_clock is supposed to be engaged to get the current device
> clock value and provide the reference for the timestamps.
> 
> Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
> 
> ---
>   v1->v4:
>      - dedicated dynamic Tx timestamp flag instead of shared with Rx
>   v4->v5:
>      - elaborated commit message
>      - more words about device clocks added,
>      - note about dedicated Rx/Tx timestamp flags added
> 
> ---
>  lib/librte_ethdev/rte_ethdev.c |  1 +
>  lib/librte_ethdev/rte_ethdev.h |  4 ++++  lib/librte_mbuf/rte_mbuf_dyn.h |
> 31 +++++++++++++++++++++++++++++++
>  3 files changed, 36 insertions(+)
> 
> diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
> index 8e10a6f..02157d5 100644
> --- a/lib/librte_ethdev/rte_ethdev.c
> +++ b/lib/librte_ethdev/rte_ethdev.c
> @@ -162,6 +162,7 @@ struct rte_eth_xstats_name_off {
>  	RTE_TX_OFFLOAD_BIT2STR(UDP_TNL_TSO),
>  	RTE_TX_OFFLOAD_BIT2STR(IP_TNL_TSO),
>  	RTE_TX_OFFLOAD_BIT2STR(OUTER_UDP_CKSUM),
> +	RTE_TX_OFFLOAD_BIT2STR(SEND_ON_TIMESTAMP),
>  };
> 
>  #undef RTE_TX_OFFLOAD_BIT2STR
> diff --git a/lib/librte_ethdev/rte_ethdev.h b/lib/librte_ethdev/rte_ethdev.h
> index a49242b..6f6454c 100644
> --- a/lib/librte_ethdev/rte_ethdev.h
> +++ b/lib/librte_ethdev/rte_ethdev.h
> @@ -1178,6 +1178,10 @@ struct rte_eth_conf {
>  /** Device supports outer UDP checksum */  #define
> DEV_TX_OFFLOAD_OUTER_UDP_CKSUM  0x00100000
> 
> +/** Device supports send on timestamp */ #define
> +DEV_TX_OFFLOAD_SEND_ON_TIMESTAMP 0x00200000
> +
> +
>  #define RTE_ETH_DEV_CAPA_RUNTIME_RX_QUEUE_SETUP 0x00000001
> /**< Device supports Rx queue setup after device started*/  #define
> RTE_ETH_DEV_CAPA_RUNTIME_TX_QUEUE_SETUP 0x00000002 diff --git
> a/lib/librte_mbuf/rte_mbuf_dyn.h b/lib/librte_mbuf/rte_mbuf_dyn.h index
> 96c3631..8407230 100644
> --- a/lib/librte_mbuf/rte_mbuf_dyn.h
> +++ b/lib/librte_mbuf/rte_mbuf_dyn.h
> @@ -250,4 +250,35 @@ int rte_mbuf_dynflag_lookup(const char *name,
> #define RTE_MBUF_DYNFIELD_METADATA_NAME
> "rte_flow_dynfield_metadata"
>  #define RTE_MBUF_DYNFLAG_METADATA_NAME
> "rte_flow_dynflag_metadata"
> 
> +/**
> + * The timestamp dynamic field 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 Tx 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.
> + *
> + * After PKT_RX_TIMESTAMP flag and fixed timestamp field deprecation
> + * and obsoleting, the dedicated Rx timestamp flag is supposed to be
> + * introduced and the shared dynamic timestamp field will be used
> + * to handle the timestamps on receiving datapath as well.
> + */
> +#define RTE_MBUF_DYNFIELD_TIMESTAMP_NAME
> "rte_dynfield_timestamp"
> +
> +/**
> + * When PMD sees the RTE_MBUF_DYNFLAG_TX_TIMESTAMP_NAME flag
> 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).
> + *
> + * There is no any packet reordering according to timestamps is
> +supposed,
> + * neither for packet within the burst, nor for the whole bursts, it is
> + * an entirely application responsibility to generate packets and its
> + * timestamps in desired order. The timestamps might be put only in
> + * the first packet in the burst providing the entire burst scheduling.
> + */
> +#define RTE_MBUF_DYNFLAG_TX_TIMESTAMP_NAME
> "rte_dynflag_tx_timestamp"
> +
>  #endif
> --
> 1.8.3.1