netdev - Re: [PATCH v2 1/1] VSOCK: remove more space available check filling TX vq

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Message-ID: <20160815142921.GC3598@stefanha-x1.localdomain>
Date:	Mon, 15 Aug 2016 15:29:21 +0100
From:	Stefan Hajnoczi <stefanha@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	ggarcia@...a.uab.cat, netdev@...r.kernel.org
Subject: Re: [PATCH v2 1/1] VSOCK: remove more space available check filling
 TX vq

On Mon, Aug 15, 2016 at 02:16:51AM +0300, Michael S. Tsirkin wrote:
> On Wed, Aug 10, 2016 at 05:24:34PM +0200, ggarcia@...a.uab.cat wrote:
> > From: Gerard Garcia <ggarcia@...c.uab.cat>
> > 
> > Remove unnecessary use of enable/disable callback notifications
> > and the incorrect more space available check.
> > 
> > The virtio_transport_tx_work handles when the TX virtqueue
> > has more buffers available.
> > 
> > Signed-off-by: Gerard Garcia <ggarcia@...c.uab.cat>
> > Acked-by: Stefan Hajnoczi <stefanha@...hat.com>
> 
> Generally enable/disable is a worthwhile optimization,
> but if Stefan wants to keep code simple for now,
> I don't have a problem with that.

Enabling/disabling callbacks is inappropriate in this function because
its job is *submitting* buffers rather than *reclaiming* completed
buffers.  Oops, I'm not sure how this mistake crept in :).

The callback suppression should only be done around the loop that
reclaims buffers.  Doing it in the wrong place leads to hangs if
interrupts are lost.

Stefan

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