netdev - Re: NAPI rescheduling and the delay caused by it

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Message-ID: <1386199931.30495.139.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 04 Dec 2013 15:32:11 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	Malcolm Crossley <malcolm.crossley@...rix.com>,
	Jonathan Davies <Jonathan.Davies@...citrix.com>,
	Paul Durrant <Paul.Durrant@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>,
	Ian Campbell <Ian.Campbell@...rix.com>
Subject: Re: NAPI rescheduling and the delay caused by it

On Wed, 2013-12-04 at 21:23 +0000, Zoltan Kiss wrote:

> I see netif_rx_ni makes sure the softirq is executed, but I'm not sure I 
> get how is it related to wake_queue. Can you explain a bit more?
> 

Calling netif_wake_queue() from process context makes no guarantee the
TX softirq is processed in the following cycles.

This interface is meant to be used from softirq context.


Try to enclose it in :

void xenvif_notify_tx_completion(struct xenvif *vif)
{
	if (netif_queue_stopped(vif->dev) && xenvif_rx_schedulable(vif)) {
		local_bh_disable();
		netif_wake_queue(vif->dev);
		local_bh_enable();
	}
}


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