If I read this right. You are running this on localhost (according to SO code). If that's the case, there is no actual network, and no actual TCP stack... UDP or TCP won't make a difference then, and neither will any TCP tweaking. I think this rules out the network, the switch, the NICs, and most of the OS's network stack.
Now you're looking at the JVM, the OS scheduling, power management, cache behavior, etc. Some more things to play with to rule out or find some insight: - Rule out de-optimization (you may be de-optimizing when the if (totalMessagesSent == WARMUP) triggers). Do this by examining at -XX:+PrintCompilation output - Rule out scheduling and cpu migration effects: use isolcpus and pin your processes to specific cores - How do you know that your actually disabled all power management. I'd monitor cstate and pstate to see what they actually are over time. Cool anecdote: We once had a case where something in the system was mysteriously elevating cstate away from 0 after we set to to 0. We never did find out what it was. The case was "resolved" with a cron job that set cstate to 0 every minute (yuck. I know). - Slew with different interval time in your tests to find out how long the interval needs to be before you see the perf drop. The value at which this effect starts may be an interesting hint On Wednesday, April 12, 2017 at 12:56:22 PM UTC-7, J Crawford wrote: > > The SO question has the source codes of a simple server and client that > demonstrate and isolate the problem. Basically I'm timing the latency of a > ping-pong (client-server-client) message. I start by sending one message > every 1 millisecond. I wait for 200k messages to be sent so that the > HotSpot has a chance to optimize the code. Then I change my pause time from > 1 millisecond to 30 seconds. For my surprise my write and read operation > become considerably slower. > > I don't think it is a JIT/HotSpot problem. I was able to pinpoint the > slower method to the native JNI calls to write (write0) and read. Even if I > change the pause from 1 millisecond to 1 second, problem persists. > > I was able to observe that on MacOS and Linux. > > Does anyone here have a clue of what can be happening? > > Note that I'm disabling Nagle's Algorithm with setTcpNoDelay(true). > > SO question with code and output: > http://stackoverflow.com/questions/43377600/socketchannel-why-if-i-write-msgs-quickly-the-latency-of-each-message-is-low-b > > Thanks! > > -JC > -- You received this message because you are subscribed to the Google Groups "mechanical-sympathy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
