On Mon, Mar 15, 2021 at 2:29 AM Yunsheng Lin <linyunsh...@huawei.com> wrote: > > 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.
What's the benefit here? Since qdisc->q.lock is also per-qdisc, so there is no actual contention to take it when we already acquire q->seqlock, right? Also, is ->seqlock supposed to be used for protecting skb_bad_txq etc.? From my understanding, it was introduced merely for replacing __QDISC_STATE_RUNNING. If you want to extend it, you probably have to rename it too. Thanks.
