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Thank you.
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<div class="">To make your benchmark more interesting, I would suggest varying both the number of producers and consumers as well as the number of queues they contend over (e.g. 100,000 queues with 1 producer and 1 consumer each, 1000 queues with 100 producers
and 100 consumers each etc.). This would also give you a sense of the kinds of benchmarks we’re using.
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<div class="">BTW, the impact on throughput that context switching has on message passing systems is related to the ratio between the average context switching duration and the average wait-time between messages, i.e. context-switching needs to be efficient
only to the point that it is significantly smaller than the wait-time between messages. Once it’s small enough *in comparison*, reducing it further has little impact (see calculation here:
<a href="https://inside.java/2020/08/07/loom-performance/" class="">https://inside.java/2020/08/07/loom-performance/</a>).</div>
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<div class="">— Ron<br class="">
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<div class="">On 4 Jan 2023, at 04:59, robert engels <<a href="mailto:rengels@ix.netcom.com" class="">rengels@ix.netcom.com</a>> wrote:</div>
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For some further data points. Using VthreadTest <a href="https://urldefense.com/v3/__https://github.com/robaho/vthread_test__;!!ACWV5N9M2RV99hQ!LFEPXV7dMYdKXhq8nPYKdugapqZ6YjxQ4-sIlUyqDBSyiNDaUEdmYFml7BXnDnv5A_d0yPXv-AoIPZanNQ$" class="">here</a> (essentially
a message passing system):
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<div class="">With 32 producers, 32 consumers, 500k messages on an 4/8 core machine:</div>
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<div class="">1a. native threads w ABQ: 60-65% system cpu, 20% user cpu, 15-20% idle, total time 189 seconds</div>
<div class="">1b. vthreads w ABQ: 5-10% system cpu, 75% user cpu, 15% idle, total time 63 seconds</div>
<div class="">2a. native threads w RingBuffer, spin=1: 70% system cpu, 30% user cpu, 0% idle, total time 174 seconds</div>
<div class="">2b. vthreads w RingBuffer, spin=1: 13% system cpu, 85% user, 2% idle, total time 37 seconds</div>
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<div style="caret-color: rgb(0, 0, 0);" class="">3a. native threads w RingBuffer, spin=32: 68% system cpu, 30% user cpu, 2% idle, total time 164 seconds</div>
<div style="caret-color: rgb(0, 0, 0);" class="">3b. vthreads w RingBuffer, spin=32: 13% system cpu, 85% user, 3% idle, total time 40 seconds</div>
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<div style="caret-color: rgb(0, 0, 0);" class="">(ABQ is stdlib ArrayBlockingQueue)</div>
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<div style="caret-color: rgb(0, 0, 0);" class="">The above times have a lot of variance which is not fully accounted for but the interesting thing is that the RingBuffer makes such a huge difference between 1 & 2.</div>
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<div style="caret-color: rgb(0, 0, 0);" class="">Even in 2b, there is 13% taken up by the OS - I assume due to thread switching as there is no IO in the test, which means the scheduling can probably be improved.</div>
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<div style="caret-color: rgb(0, 0, 0);" class="">I would expect a green thread system to approach 0% idle and 0% system utilization in this type of test. I am “fairly cetain” the code should able to use all carrier threads 100%. Maybe the system % is going
to something else? (You can use the SpinTest - comment out the println - and see that 100% cpu bound “do nothing” test that allocates no objects still uses more than 25% system cpu - which seems odd).</div>
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<div style="caret-color: rgb(0, 0, 0);" class="">Here is a async profile capture of 3b:</div>
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<div style="caret-color: rgb(0, 0, 0);" class=""><span id="cid:CE85336B-FD0B-40A9-9616-4944823FCAAC"><PastedGraphic-3.png></span></div>
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<div class="">Notice that the vast majority of the time is used in internal context switching.</div>
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<div class="">I can “fairly agree” with the project’s stated bias towards server systems with 1000’s of threads (I do think 1000’s of threads is enough vs. millions of threads), but I hope this can be addressed moving forward. I think the CSP (communicating
sequential processes) model (close to Actor model) simplifies a lot of concurrent programming concerns but it requires highly efficient context switching and queues to work well.</div>
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