Commit 808e7ac0 authored Oct 01, 2014 by Jesper Dangaard Brouer Committed by David S. Miller Oct 03, 2014

qdisc: dequeue bulking also pickup GSO/TSO packets



The TSO and GSO segmented packets already benefit from bulking
on their own.

The TSO packets have always taken advantage of the only updating
the tailptr once for a large packet.

The GSO segmented packets have recently taken advantage of
bulking xmit_more API, via merge commit 53fda7f7 ("Merge
branch 'xmit_list'"), specifically via commit 7f2e870f ("net:
Move main gso loop out of dev_hard_start_xmit() into helper.")
allowing qdisc requeue of remaining list.  And via commit
ce93718f ("net: Don't keep around original SKB when we
software segment GSO frames.").

This patch allow further bulking of TSO/GSO packets together,
when dequeueing from the qdisc.

Testing:
 Measuring HoL (Head-of-Line) blocking for TSO and GSO, with
netperf-wrapper. Bulking several TSO show no performance regressions
(requeues were in the area 32 requeues/sec).

Bulking several GSOs does show small regression or very small
improvement (requeues were in the area 8000 requeues/sec).

 Using ixgbe 10Gbit/s with GSO bulking, we can measure some additional
latency. Base-case, which is "normal" GSO bulking, sees varying
high-prio queue delay between 0.38ms to 0.47ms.  Bulking several GSOs
together, result in a stable high-prio queue delay of 0.50ms.

 Using igb at 100Mbit/s with GSO bulking, shows an improvement.
Base-case sees varying high-prio queue delay between 2.23ms to 2.35ms

Signed-off-by: David S. Miller <davem@davemloft.net>

parent 5772e9a3

net/sched/sch_generic.c

+3 −9

Original line number	Original line	Diff line number	Diff line
	@@ -63,10 +63,6 @@ static struct sk_buff try_bulk_dequeue_skb(struct Qdisc q,
	struct sk_buff skb, tail_skb = head_skb;		struct sk_buff skb, tail_skb = head_skb;

	while (bytelimit > 0) {		while (bytelimit > 0) {
	/* For now, don't bulk dequeue GSO (or GSO segmented) pkts */
	if (tail_skb->next \|\| skb_is_gso(tail_skb))
	break;

	skb = q->dequeue(q);		skb = q->dequeue(q);
	if (!skb)		if (!skb)
	break;		break;
	@@ -76,11 +72,9 @@ static struct sk_buff try_bulk_dequeue_skb(struct Qdisc q,
	if (!skb)		if (!skb)
	break;		break;

	/* "skb" can be a skb list after validate call above		while (tail_skb->next) /* GSO list goto tail */
	* (GSO segmented), but it is okay to append it to		tail_skb = tail_skb->next;
	* current tail_skb->next, because next round will exit
	* in-case "tail_skb->next" is a skb list.
	*/
	tail_skb->next = skb;		tail_skb->next = skb;
	tail_skb = skb;		tail_skb = skb;
	}		}