From: Cong Wang <xiyou.wangcong@gmail.com>
To: Yunsheng Lin <linyunsheng@huawei.com>
Cc: David Miller <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Jamal Hadi Salim <jhs@mojatatu.com>,
Jiri Pirko <jiri@resnulli.us>,
Linux Kernel Network Developers <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
linuxarm@openeuler.org
Subject: Re: [PATCH net-next] net: sched: remove unnecessay lock protection for skb_bad_txq/gso_skb
Date: Tue, 16 Mar 2021 11:41:28 -0700 [thread overview]
Message-ID: <CAM_iQpXT+tS1NdpiF2M0hAocWJ90mxd5Wp8HoxkEhp4k9QM4hw@mail.gmail.com> (raw)
In-Reply-To: <1615800610-34700-1-git-send-email-linyunsheng@huawei.com>
On Mon, Mar 15, 2021 at 2:29 AM Yunsheng Lin <linyunsheng@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.
next prev parent reply other threads:[~2021-03-16 18:42 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-15 9:30 [PATCH net-next] net: sched: remove unnecessay lock protection for skb_bad_txq/gso_skb Yunsheng Lin
2021-03-15 23:41 ` David Miller
2021-03-16 2:40 ` Yunsheng Lin
2021-03-16 21:45 ` David Miller
2021-03-17 0:45 ` Yunsheng Lin
2021-03-16 18:43 ` Cong Wang
2021-03-17 0:50 ` Yunsheng Lin
2021-03-16 18:41 ` Cong Wang [this message]
2021-03-17 1:01 ` Yunsheng Lin
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