linux-kernel - Re: [PATCH net-next] xen-netback: Schedule NAPI from dealloc thread instead of callback

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Message-ID: <20140313101720.GA16807@zion.uk.xensource.com>
Date:	Thu, 13 Mar 2014 10:17:20 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
CC:	<ian.campbell@...rix.com>, <wei.liu2@...rix.com>,
	<xen-devel@...ts.xenproject.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <jonathan.davies@...rix.com>
Subject: Re: [PATCH net-next] xen-netback: Schedule NAPI from dealloc thread
 instead of callback

On Wed, Mar 12, 2014 at 09:04:41PM +0000, Zoltan Kiss wrote:
> If there are unconsumed requests in the ring, but there isn't enough free
> pending slots, the NAPI instance deschedule itself. As the frontend won't send
> any more interrupts in this case, it is the task of whoever release the pending
> slots to schedule the NAPI instance in this case. Originally it was done in the
> callback, but it's better at the end of the dealloc thread, otherwise there is
> a risk that the NAPI instance just deschedule itself as the dealloc thread
> couldn't release any used slot yet. However, as there are a lot of pending
> packets, NAPI will be scheduled again, and it is very unlikely that the dealloc
> thread can't release enough slots in the meantime.
> 

So this patch restores the property that "only two parties access the
ring", right?

Wei.
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