On 2021/3/17 2:43, Cong Wang wrote: > On Mon, Mar 15, 2021 at 4:42 PM David Miller <da...@redhat.com> 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. > > They are per-cpu for pfifo_fast which sets TCQ_F_CPUSTATS too.
Did you mean qdisc_lock(q) are protecting per-cpu stats for pfifo_fast too? > > Thanks. > > . >