High latency observed on ping/pong test with low message rates

[YuanYuYuan]

Describe the bug

As titled.

• The normal

32 bytes: seq=94 rtt=40µs lat=20µs
32 bytes: seq=95 rtt=39µs lat=19µs
32 bytes: seq=96 rtt=47µs lat=23µs
32 bytes: seq=97 rtt=43µs lat=21µs
32 bytes: seq=98 rtt=42µs lat=21µs
32 bytes: seq=99 rtt=42µs lat=21µs

• After applying the patch

32 bytes: seq=93 rtt=343µs lat=171µs
32 bytes: seq=94 rtt=393µs lat=196µs
32 bytes: seq=95 rtt=423µs lat=211µs
32 bytes: seq=96 rtt=368µs lat=184µs
32 bytes: seq=97 rtt=652µs lat=326µs
32 bytes: seq=98 rtt=550µs lat=275µs
32 bytes: seq=99 rtt=418µs lat=209µs

To reproduce

diff --git a/examples/examples/z_ping.rs b/examples/examples/z_ping.rs
index 9f715ea15..d0ccbc0ec 100644
--- a/examples/examples/z_ping.rs
+++ b/examples/examples/z_ping.rs
@@ -56,6 +56,7 @@ fn main() {
     }
 
     for _ in 0..n {
+        std::thread::sleep(std::time::Duration::from_millis(200));
         let data = data.clone();
         let write_time = Instant::now();
         publisher.put(data).wait().unwrap();

System info

• zenoh 77923a2

[YuanYuYuan]

This is an identified issue due to cache or OS scheduling issues. See this report for more details. https://zenoh.io/blog/2021-07-13-zenoh-performance-async/#peer-to-peer-communication