netdev - Re: [RFC PATCH V2 3/8] netback: switch to NAPI + kthread model

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Date:	Tue, 17 Jan 2012 17:11:57 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Stephen Hemminger <shemminger@...tta.com>
CC:	<wei.liu2@...rix.com>, Ian Campbell <Ian.Campbell@...rix.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Paul Durrant <Paul.Durrant@...rix.com>
Subject: Re: [RFC PATCH V2 3/8] netback: switch to NAPI + kthread model

On Tue, 2012-01-17 at 17:07 +0000, Stephen Hemminger wrote:
> On Tue, 17 Jan 2012 13:46:59 +0000
> Wei Liu <wei.liu2@...rix.com> wrote:
> 
> > This patch implements 1:1 model netback. We utilizes NAPI and kthread
> > to do the weight-lifting job:
> > 
> >   - NAPI is used for guest side TX (host side RX)
> >   - kthread is used for guest side RX (host side TX)
> > 
> > This model provides better scheduling fairness among vifs. It also
> > lays the foundation for future work.
> > 
> > The major defect for the current implementation is that in the NAPI
> > poll handler we don't actually disable interrupt. Xen stuff is
> > different from real hardware, it requires some other tuning of ring
> > macros.
> > 
> > Signed-off-by: Wei Liu <wei.liu2@...rix.com>
> 
> The network receive processing is sensitive to the context it is run in.
> Normally it is run in softirq with interrupts enabled. With your code,
> the poll routine disables IRQ's which shouldn't be necessary.
> 

Misunderstanding here. I should rewrite my commit message.

By "disabling interrupt" I mean stop the other end from generating
events, not system wide disabling interrupt.

> Why does xenvif_receive_skb() need to still exist? Couldn't it
> just be replaced with call to netif_receive_skb() in one place it is called.

Sure.


Wei.

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