NAME<\/a> ETF \u2212 Earliest TxTime First (ETF) Qdisc<\/p>\n tc qdisc … dev<\/b> dev parent<\/b> classid [ handle<\/b> major: ] etf clockid<\/b> clockid [ delta<\/b> delta_nsecs ] [ deadline_mode ] [ offload ]<\/b><\/p>\n The ETF (Earliest TxTime First) qdisc allows applications to control the instant when a packet should be dequeued from the traffic control layer into the netdevice. If offload<\/b> is configured and supported by the network interface card, the it will also control when packets leave the network controller.<\/p>\n ETF achieves that by buffering packets until a configurable time before their transmission time (i.e. txtime, or deadline), which can be configured through the delta<\/b> option.<\/p>\n The qdisc uses a rb-tree internally so packets are always \u2019ordered\u2019 by their txtime and will be dequeued following the (next) earliest txtime first.<\/p>\n It relies on the SO_TXTIME socket option and the SCM_TXTIME CMSG in each packet field to configure the behavior of time dependent sockets: the clockid to be used as a reference, if the expected mode of txtime for that socket is deadline or strict mode, and if packet drops should be reported on the socket\u2019s error queue. See socket(7)<\/b> for more information.<\/p>\n The etf qdisc will drop any packets with a txtime in the past, or if a packet expires while waiting for being dequeued.<\/p>\n This queueing discipline is intended to be used by TSN (Time Sensitive Networking) applications, and it exposes a traffic shaping functionality that is commonly documented as “Launch Time” or “Time-Based Scheduling” by vendors and the documentation of network interface controllers.<\/p>\n ETF is meant to be installed under another qdisc that maps packet flows to traffic classes, one example is mqprio(8).<\/b><\/p>\n clockid<\/p>\n Specifies the clock to be used by qdisc\u2019s internal timer for measuring time and scheduling events. The qdisc expects that packets passing through it to be using this same clockid<\/b> as the reference of their txtime timestamps. It will drop packets coming from sockets that do not comply with that.<\/p>\n For more information about time and clocks on Linux, please refer to time(7)<\/b> and clock_gettime(3).<\/b><\/p>\n delta<\/p>\n<\/td>\n After enqueueing or dequeueing a packet, the qdisc will schedule its next wake-up time for the next txtime minus this delta value. This means delta<\/b> can be used as a fudge factor for the scheduler latency of a system. This value must be specified in nanoseconds. The default value is 0 nanoseconds.<\/p>\n<\/td>\n<\/tr>\n<\/table>\n deadline_mode<\/p>\n When deadline_mode<\/b> is set, the qdisc will handle txtime with a different semantics, changed from a \u2019strict\u2019 transmission time to a deadline. In practice, this means during the dequeue flow etf(8)<\/b> will set the txtime of the packet being dequeued to \u2019now\u2019. The default is for this option to be disabled.<\/p>\n offload<\/p>\n When offload<\/b> is set, etf(8)<\/b> will try to configure the network interface so time-based transmission arbitration is enabled in the controller. This feature is commonly referred to as “Launch Time” or “Time-Based Scheduling” by the documentation of network interface controllers. The default is for this option to be disabled.<\/p>\n skip_sock_check<\/p>\n etf(8)<\/b> currently drops any packet which does not have a socket associated with it or if the socket does not have SO_TXTIME socket option set. But, this will not work if the launchtime is set by another entity inside the kernel (e.g. some other Qdisc). Setting the skip_sock_check will skip checking for a socket associated with the packet.<\/p>\n ETF is used to enforce a Quality of Service. It controls when each packets should be dequeued and transmitted, and can be used for limiting the data rate of a traffic class. To separate packets into traffic classes the user may choose mqprio(8),<\/b> and configure it like this:<\/p>\n # tc qdisc add dev eth0 handle 100: parent root mqprio num_tc 3 <\/p>\n
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