Re: [Xen-devel] [PATCH net V2] xen-netback: don't move event pointer in TX credit timeout callback

On Thu, May 15, 2014 at 02:40:58PM +0100, David Vrabel wrote:

On 15/05/14 12:59, Wei Liu wrote:

quoted

... otherwise the frontend will try to send TX event all the time, even
if no progress can be made. The pointer should only be advanced by the
routine that actually processes the ring (that is, xenvif_poll).

No it does not.  RING_FINAL_CHECK_FOR_REQUESTS() only advances the event
index if the ring is empty.

This will also result in xenvif_up() failing to properly enable the event.

I think Jacek's bug may be that netback fails to call napi_complete()
when credit is exceeded and there still outstanding requests on the
from-guest ring and thus napi repeatedly polls.

Correct. We should call napi_complete if this vif is rate limited.

Wei.