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[
    {
        "id": 115373,
        "web_url": "https://patches.dpdk.org/comment/115373/",
        "msgid": "<20200707143251.GJ5869@platinum>",
        "date": "2020-07-07T14:32:51",
        "subject": "Re: [dpdk-dev] [PATCH v3 1/2] mbuf: introduce accurate packet Tx\n\tscheduling",
        "submitter": {
            "id": 8,
            "url": "https://patches.dpdk.org/api/people/8/?format=api",
            "name": "Olivier Matz",
            "email": "olivier.matz@6wind.com"
        },
        "content": "On Tue, Jul 07, 2020 at 01:08:02PM +0000, Viacheslav Ovsiienko wrote:\n> There is the requirement on some networks for precise traffic timing\n> management. The ability to send (and, generally speaking, receive)\n> the packets at the very precisely specified moment of time provides\n> the opportunity to support the connections with Time Division\n> Multiplexing using the contemporary general purpose NIC without involving\n> an auxiliary hardware. For example, the supporting of O-RAN Fronthaul\n> interface is one of the promising features for potentially usage of the\n> precise time management for the egress packets.\n> \n> The main objective of this RFC is to specify the way how applications\n> can provide the moment of time at what the packet transmission must be\n> started and to describe in preliminary the supporting this feature from\n> mlx5 PMD side.\n> \n> The new dynamic timestamp field is proposed, it provides some timing\n> information, the units and time references (initial phase) are not\n> explicitly defined but are maintained always the same for a given port.\n> Some devices allow to query rte_eth_read_clock() that will return\n> the current device timestamp. The dynamic timestamp flag tells whether\n> the field contains actual timestamp value. For the packets being sent\n> this value can be used by PMD to schedule packet sending.\n> \n> After PKT_RX_TIMESTAMP flag and fixed timestamp field deprecation\n> and obsoleting, these dynamic flag and field will be used to manage\n> the timestamps on receiving datapath as well.\n> \n> When PMD sees the \"rte_dynfield_timestamp\" set on the packet being sent\n> it tries to synchronize the time of packet appearing on the wire with\n> the specified packet timestamp. If the specified one is in the past it\n> should be ignored, if one is in the distant future it should be capped\n> with some reasonable value (in range of seconds). These specific cases\n> (\"too late\" and \"distant future\") can be optionally reported via\n> device xstats to assist applications to detect the time-related\n> problems.\n> \n> There is no any packet reordering according timestamps is supposed,\n> neither within packet burst, nor between packets, it is an entirely\n> application responsibility to generate packets and its timestamps\n> in desired order. The timestamps can be put only in the first packet\n> in the burst providing the entire burst scheduling.\n> \n> PMD reports the ability to synchronize packet sending on timestamp\n> with new offload flag:\n> \n> This is palliative and is going to be replaced with new eth_dev API\n> about reporting/managing the supported dynamic flags and its related\n> features. This API would break ABI compatibility and can't be introduced\n> at the moment, so is postponed to 20.11.\n> \n> For testing purposes it is proposed to update testpmd \"txonly\"\n> forwarding mode routine. With this update testpmd application generates\n> the packets and sets the dynamic timestamps according to specified time\n> pattern if it sees the \"rte_dynfield_timestamp\" is registered.\n> \n> The new testpmd command is proposed to configure sending pattern:\n> \n> set tx_times <burst_gap>,<intra_gap>\n> \n> <intra_gap> - the delay between the packets within the burst\n>               specified in the device clock units. The number\n>               of packets in the burst is defined by txburst parameter\n> \n> <burst_gap> - the delay between the bursts in the device clock units\n> \n> As the result the bursts of packet will be transmitted with specific\n> delays between the packets within the burst and specific delay between\n> the bursts. The rte_eth_get_clock is supposed to be engaged to get the\n> current device clock value and provide the reference for the timestamps.\n> \n> Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>\n> ---\n>  lib/librte_ethdev/rte_ethdev.c |  1 +\n>  lib/librte_ethdev/rte_ethdev.h |  4 ++++\n>  lib/librte_mbuf/rte_mbuf_dyn.h | 32 ++++++++++++++++++++++++++++++++\n>  3 files changed, 37 insertions(+)\n> \n> diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c\n> index 8e10a6f..02157d5 100644\n> --- a/lib/librte_ethdev/rte_ethdev.c\n> +++ b/lib/librte_ethdev/rte_ethdev.c\n> @@ -162,6 +162,7 @@ struct rte_eth_xstats_name_off {\n>  \tRTE_TX_OFFLOAD_BIT2STR(UDP_TNL_TSO),\n>  \tRTE_TX_OFFLOAD_BIT2STR(IP_TNL_TSO),\n>  \tRTE_TX_OFFLOAD_BIT2STR(OUTER_UDP_CKSUM),\n> +\tRTE_TX_OFFLOAD_BIT2STR(SEND_ON_TIMESTAMP),\n>  };\n>  \n>  #undef RTE_TX_OFFLOAD_BIT2STR\n> diff --git a/lib/librte_ethdev/rte_ethdev.h b/lib/librte_ethdev/rte_ethdev.h\n> index a49242b..6f6454c 100644\n> --- a/lib/librte_ethdev/rte_ethdev.h\n> +++ b/lib/librte_ethdev/rte_ethdev.h\n> @@ -1178,6 +1178,10 @@ struct rte_eth_conf {\n>  /** Device supports outer UDP checksum */\n>  #define DEV_TX_OFFLOAD_OUTER_UDP_CKSUM  0x00100000\n>  \n> +/** Device supports send on timestamp */\n> +#define DEV_TX_OFFLOAD_SEND_ON_TIMESTAMP 0x00200000\n> +\n> +\n>  #define RTE_ETH_DEV_CAPA_RUNTIME_RX_QUEUE_SETUP 0x00000001\n>  /**< Device supports Rx queue setup after device started*/\n>  #define RTE_ETH_DEV_CAPA_RUNTIME_TX_QUEUE_SETUP 0x00000002\n> diff --git a/lib/librte_mbuf/rte_mbuf_dyn.h b/lib/librte_mbuf/rte_mbuf_dyn.h\n> index 96c3631..5b2f3da 100644\n> --- a/lib/librte_mbuf/rte_mbuf_dyn.h\n> +++ b/lib/librte_mbuf/rte_mbuf_dyn.h\n> @@ -250,4 +250,36 @@ int rte_mbuf_dynflag_lookup(const char *name,\n>  #define RTE_MBUF_DYNFIELD_METADATA_NAME \"rte_flow_dynfield_metadata\"\n>  #define RTE_MBUF_DYNFLAG_METADATA_NAME \"rte_flow_dynflag_metadata\"\n>  \n> +/**\n> + * The timestamp dynamic field provides some timing information, the\n> + * units and time references (initial phase) are not explicitly defined\n> + * but are maintained always the same for a given port. Some devices allow\n> + * to query rte_eth_read_clock() that will return the current device\n> + * timestamp. The dynamic Tx timestamp flag tells whether the field contains\n> + * actual timestamp value. For the packets being sent this value can be\n> + * used by PMD to schedule packet sending.\n> + *\n> + * After PKT_RX_TIMESTAMP flag and fixed timestamp field deprecation\n> + * and obsoleting, the dedicated Rx timestamp flag is supposed to be\n> + * introduced and the shared timestamp field will be used to handle the\n> + * timestamps on receiving datapath as well. Having the dedicated flags\n> + * for Rx/Tx timstamps allows applications not to perform explicit flags\n> + * reset on forwarding and not to promote received timestamps to the\n> + * transmitting datapath by default.\n> + *\n> + * When PMD sees the RTE_MBUF_DYNFLAG_TX_TIMESTAMP_NAME flag set on the\n> + * packet being sent it tries to synchronize the time of packet appearing\n> + * on the wire with the specified packet timestamp. If the specified one\n> + * is in the past it should be ignored, if one is in the distant future\n> + * it should be capped with some reasonable value (in range of seconds).\n> + *\n> + * There is no any packet reordering according timestamps is supposed,\n\nI think there is a typo here\n\n> + * neither within packet burst, nor between packets, it is an entirely\n> + * application responsibility to generate packets and its timestamps in\n> + * desired order. The timestamps might be put only in the first packet in\n> + * the burst providing the entire burst scheduling.\n> + */\n> +#define RTE_MBUF_DYNFIELD_TIMESTAMP_NAME \"rte_dynfield_timestamp\"\n> +#define RTE_MBUF_DYNFLAG_TX_TIMESTAMP_NAME \"rte_dynflag_tx_timestamp\"\n\nIs it possible to split the comment, to document both\nRTE_MBUF_DYNFIELD_TIMESTAMP_NAME and RTE_MBUF_DYNFLAG_TX_TIMESTAMP_NAME ?  I\ndidn't try to generate the documentation, but I think, like this, that\nRTE_MBUF_DYNFLAG_TX_TIMESTAMP_NAME will be undocumented.\n\nApart from that, it looks good to me.\n\n\n> +\n>  #endif\n> -- \n> 1.8.3.1\n>",
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            "References": "<1591771085-24959-1-git-send-email-viacheslavo@mellanox.com>\n <1594127283-19863-1-git-send-email-viacheslavo@mellanox.com>",
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            "From": "Olivier Matz <olivier.matz@6wind.com>",
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            "Subject": "Re: [dpdk-dev] [PATCH v3 1/2] mbuf: introduce accurate packet Tx\n\tscheduling",
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            "Date": "Tue, 7 Jul 2020 16:32:51 +0200",
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