On 2021/3/16 7:41, David Miller wrote: > From: Yunsheng Lin <linyunsh...@huawei.com> > Date: Mon, 15 Mar 2021 17:30:10 +0800 > >> Currently qdisc_lock(q) is taken before enqueuing and dequeuing >> for lockless qdisc's skb_bad_txq/gso_skb queue, qdisc->seqlock is >> also taken, which can provide the same protection as qdisc_lock(q). >> >> This patch removes the unnecessay qdisc_lock(q) protection for >> lockless qdisc' skb_bad_txq/gso_skb queue. >> >> And dev_reset_queue() takes the qdisc->seqlock for lockless qdisc >> besides taking the qdisc_lock(q) when doing the qdisc reset, >> some_qdisc_is_busy() takes both qdisc->seqlock and qdisc_lock(q) >> when checking qdisc status. It is unnecessary to take both lock >> while the fast path only take one lock, so this patch also changes >> it to only take qdisc_lock(q) for locked qdisc, and only take >> qdisc->seqlock for lockless qdisc. >> >> Since qdisc->seqlock is taken for lockless qdisc when calling >> qdisc_is_running() in some_qdisc_is_busy(), use qdisc->running >> to decide if the lockless qdisc is running. >> >> Signed-off-by: Yunsheng Lin <linyunsh...@huawei.com> > > What about other things protected by this lock, such as statistics and qlen? > > This change looks too risky to me.
Ok, If that is the case, maybe we just remove qdisc->seqlock and use qdisc_lock(q) for lockless qdisc too, so that we do not need to worry about "lockless qdisc' other things protected by qdisc_lock(q)". At least for the fast path, taking two locks for lockless qdisc hurts performance when handling requeued skb, especially if the lockless qdisc supports TCQ_F_CAN_BYPASS. > > > . >
