Two performance-related fixes:

1. as reported by Alexander Fiveg, the allocator was reporting
   half of the allocated memory. Fix this by exiting from the
   loop earlier (not too critical because this code is going
   away soon).

2. following a discussion on freebsd-current
    http://lists.freebsd.org/pipermail/freebsd-current/2012-January/031144.html
   turns out that (re)loading the dmamap was expensive and not optimized.
   This operation is in the critical path when doing zero-copy forwarding
   between interfaces.
   At least on netmap and i386/amd64, the bus_dmamap_load can be
   completely bypassed if the map is NULL, so we do it.

The latter change gives an almost 3x improvement in forwarding
performance, from the previous 9.5Mpps at 2.9GHz to the current
line rate (14.2Mpps) at 1.733GHz. (this is for 64+4 byte packets,
in other configurations the PCIe bus is a bottleneck).

1 files changed, 3 insertions, 26 deletions

diff --git a/sys/dev/netmap/netmap.c b/sys/dev/netmap/netmap.c
index d01ed48..83077a2 100644
--- a/sys/dev/netmap/netmap.c
+++ b/sys/dev/netmap/netmap.c
@@ -426,7 +426,6 @@ netmap_dtor(void *data)
 }
 
 
-
 /*
  * Create and return a new ``netmap_if`` object, and possibly also
  * rings and packet buffors.
@@ -1393,30 +1392,6 @@ netmap_reset(struct netmap_adapter *na, enum txrx tx, int n,
 	return kring->ring->slot;
 }
 
-static void
-ns_dmamap_cb(__unused void *arg, __unused bus_dma_segment_t * segs,
-	__unused int nseg, __unused int error)
-{
-}
-
-/* unload a bus_dmamap and create a new one. Used when the
- * buffer in the slot is changed.
- * XXX buflen is probably not needed, buffers have constant size.
- */
-void
-netmap_reload_map(bus_dma_tag_t tag, bus_dmamap_t map, void *buf)
-{
-	bus_dmamap_unload(tag, map);
-	bus_dmamap_load(tag, map, buf, NETMAP_BUF_SIZE, ns_dmamap_cb,
-		NULL, BUS_DMA_NOWAIT);
-}
-
-void
-netmap_load_map(bus_dma_tag_t tag, bus_dmamap_t map, void *buf)
-{
-	bus_dmamap_load(tag, map, buf, NETMAP_BUF_SIZE, ns_dmamap_cb,
-		NULL, BUS_DMA_NOWAIT);
-}
 
 /*------ netmap memory allocator -------*/
 /*
@@ -1541,7 +1516,7 @@ netmap_memory_init(void)
 	int i, n, sz = NETMAP_MEMORY_SIZE;
 	int extra_sz = 0; // space for rings and two spare buffers
 
-	for (; !buf && sz >= 1<<20; sz >>=1) {
+	for (; sz >= 1<<20; sz >>=1) {
 		extra_sz = sz/200;
 		extra_sz = (extra_sz + 2*PAGE_SIZE - 1) & ~(PAGE_SIZE-1);
 	        buf = contigmalloc(sz + extra_sz,
@@ -1552,6 +1527,8 @@ netmap_memory_init(void)
 			     PAGE_SIZE, /* alignment */
 			     0 /* boundary */
 			    );
+		if (buf)
+			break;
 	} 
 	if (buf == NULL)
 		return (ENOMEM);