From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sowmini Varadhan Subject: [PATCH net-next v2 2/2] Re-check for a VIO_DESC_READY data descriptor after short udelay() Date: Tue, 2 Sep 2014 12:20:29 -0400 Message-ID: <20140902162029.GC31516@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org To: davem@davemloft.net, raghuram.kothakota@oracle.com, sowmini.varadhan@oracle.com Return-path: Received: from userp1040.oracle.com ([156.151.31.81]:26065 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751295AbaIBQUo (ORCPT ); Tue, 2 Sep 2014 12:20:44 -0400 Content-Disposition: inline Sender: netdev-owner@vger.kernel.org List-ID: Upon encountering the first !VIO_DESC_READY in vnet_walk_rx(), it is frequently worthwhile to re-check the descriptor status after a short microsecond delay, as a bursty sender could be actively populating the descriptors, and the short udelay() is far less expensive than rolling back to ldc_rx() and having to wake up and read data on another LDC message. Signed-off-by: Sowmini Varadhan Acked-by: Raghuram Kothakota --- changes since v1: moved label `again', variable `retries' to this patchset. drivers/net/ethernet/sun/sunvnet.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) diff --git a/drivers/net/ethernet/sun/sunvnet.c b/drivers/net/ethernet/sun/sunvnet.c index 8f90b57..7b1f320 100644 --- a/drivers/net/ethernet/sun/sunvnet.c +++ b/drivers/net/ethernet/sun/sunvnet.c @@ -390,11 +390,28 @@ static int vnet_walk_rx(struct vnet_port *port, struct vio_dring_state *dr, viodbg(DATA, "vnet_walk_rx start[%08x] end[%08x]\n", start, end); while (start != end) { - int ack = 0, err = vnet_walk_rx_one(port, dr, start, &ack); + int retries; + int ack = 0, err; + + retries = 0; +again: + err = vnet_walk_rx_one(port, dr, start, &ack); if (err == -ECONNRESET) return err; - if (err != 0) - break; + if (err != 0) { + /* The descriptor was not READY. Retry with a + * small delay, in case we have a bursty sender + * that is actively populating the descriptors, to + * reduce the overhead of stopping and re-entering + * which would involve expensive LDC messages. + */ + if (retries++ < 3) { + udelay(4); + goto again; + } else { + break; + } + } if (ack_start == -1) ack_start = start; ack_end = start; -- 1.8.4.2