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

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Message-ID: <CAK-6q+jeubhGah2gG1JJxfmOW=sNdMrLf+mk_a3X_r+Na=tHXg@mail.gmail.com>
Date:   Wed, 11 May 2022 09:09:40 -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 Tue, May 10, 2022 at 10:52 AM Miquel Raynal
<miquel.raynal@...tlin.com> wrote:
>
> Hi Alex,
>
> > > --- 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?
>
> That's actually a good idea. I've implemented it and it looks nice too.
> I'll clean this up and share a new version with:
> - The wake call checked everytime hold_txs gets decremented
> - The removal of the _queue_is_held() helper
> - _wake/stop_queue() turned static
> - _hold/release_queue() used everywhere
>

I think there is also a lock necessary for atomic inc/dec hitting zero
and the stop/wake call afterwards... ,there are also a lot of
optimization techniques to only hold the lock for hitting zero cases
in such areas. However we will see...

- Alex