netdev - Re: [WIP] net+mlx4: auto doorbell

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Message-ID: <1480560655.18162.255.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Wed, 30 Nov 2016 18:50:55 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Tom Herbert <tom@...bertland.com>
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Rick Jones <rick.jones2@....com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Achiad Shochat <achiad@...lanox.com>
Subject: Re: [WIP] net+mlx4: auto doorbell

On Wed, 2016-11-30 at 18:32 -0800, Eric Dumazet wrote:

> I simply suggest we try to queue the qdisc for further servicing as we
> do today, from net_tx_action(), but we might use a different bit, so
> that we leave the opportunity for another cpu to get __QDISC_STATE_SCHED
> before we grab it from net_tx_action(), maybe 100 usec later (time to
> flush all skbs queued in napi_consume_skb() and maybe RX processing,
> since most NIC handle TX completion before doing RX processing from thei
> napi poll handler.
> 
> Should be doable with few changes in __netif_schedule() and
> net_tx_action(), plus some control paths that will need to take care of
> the new bit at dismantle time, right ?

Hmm... this is silly. Code already implements a different bit.

qdisc_run() seems to run more often from net_tx_action(), I have to find
out why.