Re: [Xen-devel] NAPI rescheduling and the delay caused by it

[Eric Dumazet <eric.dumazet@xxxxxxxxx>]

On Wed, 2013-12-04 at 18:55 +0000, Zoltan Kiss wrote:

> So, my questions are:
> - why is NAPI rescheduled on an another CPU?
> - why does it cause a 3-4 milisec delay?

NAPI can not be scheduled on another cpu.

But at the time of napi_schedule() call, napi_struct can be already be
scheduled by another cpu.

( NAPI_STATE_SCHED bit already set)

So I would say something made the 'other' cpu non responsive fast enough
to softirq events being ready for service.

(Another wakeup happened 3-4 millisec later)

Really, I suspect your usage of netif_wake_queue() is simply wrong.

Check why we have netif_rx() and netif_rx_ni() variants.

And ask yourself if xenvif_notify_tx_completion() is correct, being
called from process context.




_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel