From d9601a36ffdb5c142697bef1228afb5ba4ee4003 Mon Sep 17 00:00:00 2001 From: Paul Durrant Date: Wed, 11 Dec 2013 10:57:16 +0000 Subject: [PATCH] xen-netback: napi: don't prematurely request a tx event 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. The event pointer is updated by RING_FINAL_CHECK_FOR_REQUESTS in xenvif_poll, the napi poll function, if the work done is less than the budget i.e. when actually transitioning back to interrupt mode. Reported-by: Malcolm Crossley Signed-off-by: Paul Durrant Cc: Wei Liu Cc: Ian Campbell Cc: David Vrabel Signed-off-by: David S. Miller --- drivers/net/xen-netback/netback.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c index db79e29b3d09..33b8aa612d13 100644 --- a/drivers/net/xen-netback/netback.c +++ b/drivers/net/xen-netback/netback.c @@ -1475,7 +1475,7 @@ static unsigned xenvif_tx_build_gops(struct xenvif *vif, int budget) continue; } - RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, work_to_do); + work_to_do = RING_HAS_UNCONSUMED_REQUESTS(&vif->tx); if (!work_to_do) break;