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Date:   Thu, 13 May 2021 08:22:22 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Yunsheng Lin <linyunsheng@huawei.com>
Cc:     <davem@davemloft.net>, <olteanv@gmail.com>, <ast@kernel.org>,
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Subject: Re: [PATCH net v7 3/3] net: sched: fix tx action reschedule issue
 with stopped queue
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        <1620868260-32984-4-git-send-email-linyunsheng@huawei.com>
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On Thu, 13 May 2021 09:11:00 +0800 Yunsheng Lin wrote:
> The netdev qeueue might be stopped when byte queue limit has
> reached or tx hw ring is full, net_tx_action() may still be
> rescheduled endlessly if STATE_MISSED is set, which consumes
> a lot of cpu without dequeuing and transmiting any skb because
> the netdev queue is stopped, see qdisc_run_end().
> 
> This patch fixes it by checking the netdev queue state before
> calling qdisc_run() and clearing STATE_MISSED if netdev queue is
> stopped during qdisc_run(), the net_tx_action() is recheduled
> again when netdev qeueue is restarted, see netif_tx_wake_queue().
> 
> As there is time window betewwn netif_xmit_frozen_or_stopped()
> checking and STATE_MISSED clearing, between which STATE_MISSED
> is set by net_tx_action() scheduled by netif_tx_wake_queue(),
> so set the STATE_MISSED again if netdev queue is restarted.
> 
> Fixes: 6b3ba9146fe6 ("net: sched: allow qdiscs to handle locking")
> Reported-by: Michal Kubecek <mkubecek@suse.cz>
> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>

> @@ -35,6 +35,25 @@
>  const struct Qdisc_ops *default_qdisc_ops = &pfifo_fast_ops;
>  EXPORT_SYMBOL(default_qdisc_ops);
>  
> +static void qdisc_maybe_stop_tx(struct Qdisc *q,

nit: qdisc_maybe_clear_missed()?