Re: Packet gets stuck in NOLOCK pfifo_fast qdisc

[Paolo Abeni]

On Wed, 2020-07-08 at 13:16 -0700, Cong Wang wrote:
> On Tue, Jul 7, 2020 at 7:18 AM Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
> > So the regression with 2 pktgen threads is still relevant. 'perf' shows
> > relevant time spent into net_tx_action() and __netif_schedule().
> 
> So, touching the __QDISC_STATE_SCHED bit in __dev_xmit_skb() is
> not a good idea.
> 
> Let me see if there is any other way to fix this.

Thank you very much for the effort! I'm personally out of ideas for a
real fix that would avoid regressions. 

To be more exaustive this are the sources of overhead, as far as I can
observe them with perf:

- contention on q->state, in __netif_schedule()
- execution of net_tx_action() when there are no packet to be served

Cheers,

Paolo