This is essentially the same patch as the original patched posted at:
http://openvswitch.org/pipermail/dev/2016-January/064971.html
The original commit message:
Before this commit, emc_processing() copied a netdev_flow_key if
there was no exact-match cache (EMC) hit. This commit eliminates
the copy by constructing the netdev_flow_key in the place it would
be copied.
Found by inspection.
Shahbaz (CCed) reports that this reduces the cost of an EMC miss by
72 cycles in his test case in which the EMC is disabled.
Presumably this is similarly valuable in cases where the EMC merely
has few hits.
However, the original patch introduced a slight performance drop for the
fast path, where every packets hits the emc cache. This patch removes
the performance drop by only reloading the key variable when a miss
happens.
CC: Muhammad Shahbaz <mshah...@cs.princeton.edu>
Signed-off-by: Ben Pfaff <b...@ovn.org>
Sgned-off-by: Andy Zhou <az...@ovn.org>
---
lib/dpif-netdev.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index 205176a..94fa5ad 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -3297,7 +3297,7 @@ emc_processing(struct dp_netdev_pmd_thread *pmd, struct
dp_packet **packets,
struct packet_batch batches[], size_t *n_batches)
{
struct emc_cache *flow_cache = &pmd->flow_cache;
- struct netdev_flow_key key;
+ struct netdev_flow_key *key = &keys[0];
size_t i, n_missed = 0, n_dropped = 0;
for (i = 0; i < cnt; i++) {
@@ -3315,19 +3315,19 @@ emc_processing(struct dp_netdev_pmd_thread *pmd, struct
dp_packet **packets,
OVS_PREFETCH(dp_packet_data(packets[i+1]));
}
- miniflow_extract(packet, &key.mf);
- key.len = 0; /* Not computed yet. */
- key.hash = dpif_netdev_packet_get_rss_hash(packet, &key.mf);
+ miniflow_extract(packet, &key->mf);
+ key->len = 0; /* Not computed yet. */
+ key->hash = dpif_netdev_packet_get_rss_hash(packet, &key->mf);
- flow = emc_lookup(flow_cache, &key);
+ flow = emc_lookup(flow_cache, key);
if (OVS_LIKELY(flow)) {
- dp_netdev_queue_batches(packet, flow, &key.mf, batches,
+ dp_netdev_queue_batches(packet, flow, &key->mf, batches,
n_batches);
} else {
/* Exact match cache missed. Group missed packets together at
* the beginning of the 'packets' array. */
- packets[n_missed] = packet;
- keys[n_missed++] = key;
+ packets[n_missed++] = packet;
+ key = &keys[n_missed];
}
}
--
1.9.1
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