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Re: [Xen-devel] [PATCH net v3 2/2] xen-netback: napi: don't prematurely request a tx event

On 10/12/13 13:39, Paul Durrant wrote:
This patch changes the RING_FINAL_CHECK_FOR_REQUESTS in
xenvif_build_tx_gops to a check for RING_HAS_UNCONSUMED_REQUESTS as the
former call has the side effect of advancing the ring event pointer and
therefore inviting another interrupt from the frontend before the napi
poll has actually finished, thereby defeating the point of napi.
Reported-by: Malcolm Crossley <malcolm.crossley@xxxxxxxxxx>
Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
  drivers/net/xen-netback/netback.c |    2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/xen-netback/netback.c 
index 83b4e5b..fb512a9 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1381,7 +1381,7 @@ static unsigned xenvif_tx_build_gops(struct xenvif *vif, 
int budget)
- RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, work_to_do);
+               work_to_do = RING_HAS_UNCONSUMED_REQUESTS(&vif->tx);
                if (!work_to_do)

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