[ovs-dev] [PATCH v2] packets: Prefetch the packet metadata in cacheline1.
Bhanuprakash Bodireddy
bhanuprakash.bodireddy at intel.com
Mon Dec 4 20:10:28 UTC 2017
pkt_metadata_prefetch_init() is used to prefetch the packet metadata
before initializing the metadata in pkt_metadata_init(). This is done
for every packet in userspace datapath and is performance critical.
Commit 99fc16c0 prefetches only cachline0 and cacheline2 as the metadata
part of respective cachelines will be initialized by pkt_metadata_init().
However in VXLAN case when popping the vxlan header, netdev_vxlan_pop_header()
invokes pkt_metadata_init_tnl() which zeroes out metadata part of
cacheline1 that wasn't prefetched earlier and causes performance
degradation.
By prefetching cacheline1, 9% performance improvement is observed with
vxlan decapsulation test case for packet sizes of 118 bytes. Performance
variation is observed based on CFLAGS.
CFLAGS="-O2" CFLAGS="-O2 -msse4.2"
Master 4.667 Mpps Master 4.710 Mpps
With Patch 5.045 Mpps With Patch 5.097 Mpps
CFLAGS="-O2 -march=native" CFLAGS="-Ofast -march=native"
Master 5.072 Mpps Master 5.349 Mpps
With Patch 5.193 Mpps With Patch 5.378 Mpps
CC: Ben Pfaff <blp at ovn.org>
Fixes: 99fc16c0 ("Reorganize the pkt_metadata structure.")
Signed-off-by: Bhanuprakash Bodireddy <bhanuprakash.bodireddy at intel.com>
---
v2->v1
* Include the throughput stats with different CFLAG options.
lib/packets.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/lib/packets.h b/lib/packets.h
index 13ea46d..74bec5d 100644
--- a/lib/packets.h
+++ b/lib/packets.h
@@ -159,7 +159,8 @@ pkt_metadata_init(struct pkt_metadata *md, odp_port_t port)
}
/* This function prefetches the cachelines touched by pkt_metadata_init()
- * For performance reasons the two functions should be kept in sync. */
+ * and pkt_metadata_init_tnl(). For performance reasons the two functions
+ * should be kep in sync. */
static inline void
pkt_metadata_prefetch_init(struct pkt_metadata *md)
{
@@ -167,6 +168,10 @@ pkt_metadata_prefetch_init(struct pkt_metadata *md)
* be initialized later in pkt_metadata_init(). */
OVS_PREFETCH(md->cacheline0);
+ /* Prefetch cacheline1 as members of this cacheline will be zeroed out
+ * in pkt_metadata_init_tnl(). */
+ OVS_PREFETCH(md->cacheline1);
+
/* Prefetch cachline2 as ip_dst & ipv6_dst fields will be initialized. */
OVS_PREFETCH(md->cacheline2);
}
--
2.4.11
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