Re: [Xen-devel] [PATCH net V2] xen-netback: don't move event pointer in TX credit timeout callback
From: David Vrabel <hidden>
Date: 2014-05-15 13:41:00
On 15/05/14 12:59, Wei Liu wrote:
... 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. David
quoted hunk ↗ jump to hunk
Reported-by: Jacek Konieczny <redacted> Signed-off-by: Wei Liu <redacted> Acked-by: Ian Campbell <redacted> Cc: Paul Durrant <redacted> --- 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 7666540..8e2cbeb 100644 --- a/drivers/net/xen-netback/netback.c +++ b/drivers/net/xen-netback/netback.c@@ -658,7 +658,7 @@ void xenvif_check_rx_xenvif(struct xenvif *vif) { int more_to_do; - RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, more_to_do); + more_to_do = RING_HAS_UNCONSUMED_REQUESTS(&vif->tx); if (more_to_do) napi_schedule(&vif->napi);