[ovs-dev] [PATCH v2] ofproto-dpif-upcall: Improve concurrency by adjust flow-limit

[Tao YunXiang]

OVS uses a set of gentle mechanisms to control the number of flows in 
datapath. However, it is difficult for the number of datapath flows to 
reach a high level in a short time.

Through some tests with Apache benchmark, I found the point is that
the value of flow-limit increases too slowly, but decreases very quickly. 

This change has two improvements. One is the flow-limit will adjust more 
linearly. The other one is, when the duration is small, the flow-limit will
increase faster.

Through this change, the test result of Apache benchmark can reach 12k from 5k,
the test command is as follows:

ab -n 200000 -c 500 -r http://1.1.1.2/

v1->v2: Make flow-limit changes linearly. Add a limitation to make flow_limit
won't overflow UINT_MAX.


Signed-off-by: Tao YunXiang <taoyunxiang at cmss.chinamobile.com>
Cc: Ben Pfaff <blp at ovn.org>

---
 ofproto/ofproto-dpif-upcall.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/ofproto/ofproto-dpif-upcall.c b/ofproto/ofproto-dpif-upcall.c
index ccf97266c..805409165 100644
--- a/ofproto/ofproto-dpif-upcall.c
+++ b/ofproto/ofproto-dpif-upcall.c
@@ -963,14 +963,20 @@ udpif_revalidator(void *arg)
 
             duration = MAX(time_msec() - start_time, 1);
             udpif->dump_duration = duration;
-            if (duration > 2000) {
-                flow_limit /= duration / 1000;
-            } else if (duration > 1300) {
-                flow_limit = flow_limit * 3 / 4;
-            } else if (duration < 1000 &&
-                       flow_limit < n_flows * 1000 / duration) {
-                flow_limit += 1000;
+
+            /* Use duration as a reference, adjust the value of flow_limit,
+             * when the duration is short, increase the flow_limit, and vice
+             * versa. The purpose of using multiple conversions between int
+             * and float is to make the flow_limit change more linear. */ 
+
+            if (duration >= 1000) {
+                flow_limit = (int) ((float) (flow_limit) / (duration / 1000.0));
+            } else if (flow_limit * (1000.0 / duration) >= UINT_MAX) {
+                flow_limit = ofproto_flow_limit;
+            } else {
+                flow_limit = (int) (flow_limit * (1000.0 / duration));
             }
+
             flow_limit = MIN(ofproto_flow_limit, MAX(flow_limit, 1000));
             atomic_store_relaxed(&udpif->flow_limit, flow_limit);
 
-- 
2.17.1