Re: [RFC PATCH v2 01/10] net: sched: allow qdiscs to handle locking
From: John Fastabend <john.fastabend@gmail.com>
Date: 2016-07-14 06:45:09
On 16-07-13 11:19 PM, John Fastabend wrote:
This patch adds a flag for queueing disciplines to indicate the stack does not need to use the qdisc lock to protect operations. This can be used to build lockless scheduling algorithms and improving performance. The flag is checked in the tx path and the qdisc lock is only taken if it is not set. For now use a conditional if statement. Later we could be more aggressive if it proves worthwhile and use a static key or wrap this in a likely(). Signed-off-by: John Fastabend <redacted> ---
[...]
quoted hunk ↗ jump to hunk
@@ -3075,6 +3075,27 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q, int rc; qdisc_calculate_pkt_len(skb, q); + + if (q->flags & TCQ_F_NOLOCK) { + if (unlikely(test_bit(__QDISC_STATE_DEACTIVATED, &q->state))) { + __qdisc_drop(skb, &to_free); + rc = NET_XMIT_DROP; + } else if ((q->flags & TCQ_F_CAN_BYPASS) && !qdisc_qlen(q)) { + qdisc_bstats_cpu_update(q, skb); + __qdisc_run(q);
Reviewing these patches now and noticed this qdisc_run() is not needed.
+ if (sch_direct_xmit(skb, q, dev, txq, root_lock, true))
+ __qdisc_run(q);
+ rc = NET_XMIT_SUCCESS;
+ } else {
+ rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
+ __qdisc_run(q);
+ }
+
+ if (unlikely(to_free))
+ kfree_skb_list(to_free);
+ return rc;
+ }
+[...] Thanks, John