[PATCH] IB/ipath: fixed bug 9776 for real

The problem was that I was updating the head register multiple times in the
rcvhdrq processing loop, and setting the counter on each update.  Since that
meant that the tail register was ahead of head for all but the last update, we
would get extra interrupts.  The fix was to not write the counter value except
on the last update.

I also changed to update rcvhdrhead and rcvegrindexhead at most every 16
packets, if there were lots of packets in the queue (and of course, on the
last packet, regardless).

I also made some small cleanups while debugging this.

With these changes, xeon/monty typically sees two openib packets per interrupt
on sdp and ipoib, opteron/monty is about 1.25 pkts/intr.

I'm seeing about 3800 Mbit/s monty/xeon, and 5000-5100 opteron/monty with
netperf sdp.  Netpipe doesn't show as good as that, peaking at about 4400 on
opteron/monty sdp.  Plain ipoib xeon is about 2100+ netperf, opteron 2900+, at
128KB

Signed-off-by: olson@eng-12.pathscale.com
Signed-off-by: Bryan O'Sullivan <bos@pathscale.com>
Cc: "Michael S. Tsirkin" <mst@mellanox.co.il>
Cc: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 22 insertions, 11 deletions

diff --git a/drivers/infiniband/hw/ipath/ipath_driver.c b/drivers/infiniband/hw/ipath/ipath_driver.c
index eb745234d8c3..e2b0bc8ebaf4 100644
--- a/drivers/infiniband/hw/ipath/ipath_driver.c
+++ b/drivers/infiniband/hw/ipath/ipath_driver.c
@@ -870,7 +870,7 @@ void ipath_kreceive(struct ipath_devdata *dd)
 	const u32 maxcnt = dd->ipath_rcvhdrcnt * rsize;	/* words */
 	u32 etail = -1, l, hdrqtail;
 	struct ips_message_header *hdr;
-	u32 eflags, i, etype, tlen, pkttot = 0;
+	u32 eflags, i, etype, tlen, pkttot = 0, updegr=0;
 	static u64 totcalls;	/* stats, may eventually remove */
 	char emsg[128];
 
@@ -884,14 +884,14 @@ void ipath_kreceive(struct ipath_devdata *dd)
 	if (test_and_set_bit(0, &dd->ipath_rcv_pending))
 		goto bail;
 
-	if (dd->ipath_port0head ==
-	    (u32)le64_to_cpu(*dd->ipath_hdrqtailptr))
+	l = dd->ipath_port0head;
+	if (l == (u32)le64_to_cpu(*dd->ipath_hdrqtailptr))
 		goto done;
 
 	/* read only once at start for performance */
 	hdrqtail = (u32)le64_to_cpu(*dd->ipath_hdrqtailptr);
 
-	for (i = 0, l = dd->ipath_port0head; l != hdrqtail; i++) {
+	for (i = 0; l != hdrqtail; i++) {
 		u32 qp;
 		u8 *bthbytes;
 
@@ -1002,15 +1002,26 @@ void ipath_kreceive(struct ipath_devdata *dd)
 		l += rsize;
 		if (l >= maxcnt)
 			l = 0;
+		if (etype != RCVHQ_RCV_TYPE_EXPECTED)
+		    updegr = 1;
 		/*
-		 * update for each packet, to help prevent overflows if we
-		 * have lots of packets.
+		 * update head regs on last packet, and every 16 packets.
+		 * Reduce bus traffic, while still trying to prevent
+		 * rcvhdrq overflows, for when the queue is nearly full
 		 */
-		(void)ipath_write_ureg(dd, ur_rcvhdrhead,
-				       dd->ipath_rhdrhead_intr_off | l, 0);
-		if (etype != RCVHQ_RCV_TYPE_EXPECTED)
-			(void)ipath_write_ureg(dd, ur_rcvegrindexhead,
-					       etail, 0);
+		if (l == hdrqtail || (i && !(i&0xf))) {
+			u64 lval;
+			if (l == hdrqtail) /* want interrupt only on last */
+				lval = dd->ipath_rhdrhead_intr_off | l;
+			else
+				lval = l;
+			(void)ipath_write_ureg(dd, ur_rcvhdrhead, lval, 0);
+			if (updegr) {
+				(void)ipath_write_ureg(dd, ur_rcvegrindexhead,
+						       etail, 0);
+				updegr = 0;
+			}
+		}
 	}
 
 	pkttot += i;