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net/sched: Introduce the ETF Qdisc

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The ETF (Earliest TxTime First) qdisc uses the information added
earlier in this series (the socket option SO_TXTIME and the new
role of sk_buff->tstamp) to schedule packets transmission based
on absolute time.

For some workloads, just bandwidth enforcement is not enough, and
precise control of the transmission of packets is necessary.

Example:

$ tc qdisc replace dev enp2s0 parent root handle 100 mqprio num_tc 3 \
           map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 queues 1@0 1@1 2@2 hw 0

$ tc qdisc add dev enp2s0 parent 100:1 etf delta 100000 \
           clockid CLOCK_TAI

In this example, the Qdisc will provide SW best-effort for the control
of the transmission time to the network adapter, the time stamp in the
socket will be in reference to the clockid CLOCK_TAI and packets
will leave the qdisc "delta" (100000) nanoseconds before its transmission
time.

The ETF qdisc will buffer packets sorted by their txtime. It will drop
packets on enqueue() if their skbuff clockid does not match the clock
reference of the Qdisc. Moreover, on dequeue(), a packet will be dropped
if it expires while being enqueued.

The qdisc also supports the SO_TXTIME deadline mode. For this mode, it
will dequeue a packet as soon as possible and change the skb timestamp
to 'now' during etf_dequeue().

Note that both the qdisc's and the SO_TXTIME ABIs allow for a clockid
to be configured, but it's been decided that usage of CLOCK_TAI should
be enforced until we decide to allow for other clockids to be used.
The rationale here is that PTP times are usually in the TAI scale, thus
no other clocks should be necessary. For now, the qdisc will return
EINVAL if any clocks other than CLOCK_TAI are used.

Signed-off-by: Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Vinicius Costa Gomes 2018-07-03 15:42:53 -07:00 • committed by David S. Miller
parent 860b642b9c
commit 25db26a913
5 changed files with 414 additions and 0 deletions
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17
include/uapi/linux/pkt_sched.h
View file

@ -937,4 +937,21 @@ enum {
#define TCA_CBS_MAX (__TCA_CBS_MAX - 1)
/* ETF */
struct tc_etf_qopt {
__s32 delta;
__s32 clockid;
__u32 flags;
#define TC_ETF_DEADLINE_MODE_ON BIT(0)
};
enum {
TCA_ETF_UNSPEC,
TCA_ETF_PARMS,
__TCA_ETF_MAX,
};
#define TCA_ETF_MAX (__TCA_ETF_MAX - 1)
#endif