netdev - Re: [PATCH wpan-next 06/11] net: mac802154: Hold the transmit queue when relevant

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Message-ID: <CAK-6q+jCYDQ-rtyawz1m2Yt+ti=3d6PrhZebB=-PjcX-6L-Kdg@mail.gmail.com>
Date:   Tue, 3 May 2022 20:51:32 -0400
From:   Alexander Aring <aahringo@...hat.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Alexander Aring <alex.aring@...il.com>,
        Stefan Schmidt <stefan@...enfreihafen.org>,
        linux-wpan@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        David Girault <david.girault@...vo.com>,
        Romuald Despres <romuald.despres@...vo.com>,
        Frederic Blain <frederic.blain@...vo.com>,
        Nicolas Schodet <nico@...fr.eu.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH wpan-next 06/11] net: mac802154: Hold the transmit queue
 when relevant

Hi,

On Wed, Apr 27, 2022 at 12:54 PM Miquel Raynal
<miquel.raynal@...tlin.com> wrote:
>
> Let's create a hold_txs atomic variable and increment/decrement it when
> relevant. Currently we can use it during a suspend. Very soon we will
> also use this feature during scans.
>
> When the variable is incremented, any further wake up call will be
> skipped until the variable gets decremented back.
>
> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> ---
>  include/net/cfg802154.h      |  3 ++-
>  net/mac802154/cfg.c          |  2 ++
>  net/mac802154/ieee802154_i.h | 24 ++++++++++++++++++++++++
>  net/mac802154/tx.c           | 15 +++++++++++++++
>  net/mac802154/util.c         |  3 +++
>  5 files changed, 46 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/cfg802154.h b/include/net/cfg802154.h
> index 473ebcb9b155..043d8e4359e7 100644
> --- a/include/net/cfg802154.h
> +++ b/include/net/cfg802154.h
> @@ -214,8 +214,9 @@ struct wpan_phy {
>         /* the network namespace this phy lives in currently */
>         possible_net_t _net;
>
> -       /* Transmission monitoring */
> +       /* Transmission monitoring and control */
>         atomic_t ongoing_txs;
> +       atomic_t hold_txs;
>
>         char priv[] __aligned(NETDEV_ALIGN);
>  };
> diff --git a/net/mac802154/cfg.c b/net/mac802154/cfg.c
> index dafe02548161..0540a2b014d2 100644
> --- a/net/mac802154/cfg.c
> +++ b/net/mac802154/cfg.c
> @@ -46,6 +46,7 @@ static int ieee802154_suspend(struct wpan_phy *wpan_phy)
>         if (!local->open_count)
>                 goto suspend;
>
> +       ieee802154_hold_queue(local);
>         ieee802154_stop_queue(local);
>         synchronize_net();
>
> @@ -72,6 +73,7 @@ static int ieee802154_resume(struct wpan_phy *wpan_phy)
>                 return ret;
>
>  wake_up:
> +       ieee802154_release_queue(local);
>         ieee802154_wake_queue(local);
>         local->suspended = false;
>         return 0;
> diff --git a/net/mac802154/ieee802154_i.h b/net/mac802154/ieee802154_i.h
> index 3f59a291b481..b55fdefb0b34 100644
> --- a/net/mac802154/ieee802154_i.h
> +++ b/net/mac802154/ieee802154_i.h
> @@ -142,6 +142,30 @@ enum hrtimer_restart ieee802154_xmit_ifs_timer(struct hrtimer *timer);
>   */
>  void ieee802154_wake_queue(struct ieee802154_local *local);
>
> +/**
> + * ieee802154_hold_queue - hold ieee802154 queue
> + * @local: main mac object
> + *
> + * Hold a queue, this queue cannot be woken up while this is active.
> + */
> +void ieee802154_hold_queue(struct ieee802154_local *local);
> +
> +/**
> + * ieee802154_release_queue - release ieee802154 queue
> + * @local: main mac object
> + *
> + * Release a queue which is held. The queue can now be woken up.
> + */
> +void ieee802154_release_queue(struct ieee802154_local *local);
> +
> +/**
> + * ieee802154_queue_is_held - checks whether the ieee802154 queue is held
> + * @local: main mac object
> + *
> + * Checks whether the queue is currently held.
> + */
> +bool ieee802154_queue_is_held(struct ieee802154_local *local);
> +
>  /**
>   * ieee802154_stop_queue - stop ieee802154 queue
>   * @local: main mac object
> diff --git a/net/mac802154/tx.c b/net/mac802154/tx.c
> index 8c0bad7796ba..d088aa8119e8 100644
> --- a/net/mac802154/tx.c
> +++ b/net/mac802154/tx.c
> @@ -106,6 +106,21 @@ ieee802154_tx(struct ieee802154_local *local, struct sk_buff *skb)
>         return NETDEV_TX_OK;
>  }
>
> +void ieee802154_hold_queue(struct ieee802154_local *local)
> +{
> +       atomic_inc(&local->phy->hold_txs);
> +}
> +
> +void ieee802154_release_queue(struct ieee802154_local *local)
> +{
> +       atomic_dec(&local->phy->hold_txs);
> +}
> +
> +bool ieee802154_queue_is_held(struct ieee802154_local *local)
> +{
> +       return atomic_read(&local->phy->hold_txs);
> +}

I am not getting this, should the release_queue() function not do
something like:

if (atomic_dec_and_test(hold_txs))
      ieee802154_wake_queue(local);

I think we don't need the test of "ieee802154_queue_is_held()" here,
then we need to replace all stop_queue/wake_queue with hold and
release?

- Alex