netdev - Re: [RFC PATCH V2] New Xen netback implementation

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Date:	Mon, 30 Jan 2012 18:27:04 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.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>,
	"David Vrabel" <david.vrabel@...rix.com>,
	Paul Durrant <Paul.Durrant@...rix.com>
Subject: Re: [RFC PATCH V2] New Xen netback implementation

On Sun, 2012-01-29 at 21:37 +0000, Konrad Rzeszutek Wilk wrote:
> 
> Sure. I also did some testing with limiting the amount of CPUs and found
> that 'xl vcpu-set 0 N' make netback not work anymore :-( 
> > 
> > 

I just played with vcpu-set a bit, and I can reproduced this problem.
That's a race condition.

One possible fix is remove cond_resched() in the kernel thread. After
removing that, it fixes the problem (at least for me).


Wei.

--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -994,7 +994,7 @@ int xenvif_kthread(void *data)
                wait_event_interruptible(vif->wq,
                                         rx_work_todo(vif) ||
                                         kthread_should_stop());
-               cond_resched();
+               /* cond_resched(); */
 
                if (kthread_should_stop())
                        break;


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