[GitHub] [kafka] divijvaidya commented on pull request #13312: KAFKA-14766: Improve performance of VarInt encoding and decoding

["divijvaidya (via GitHub)" <gi...@apache.org>]

divijvaidya commented on PR #13312:
URL: https://github.com/apache/kafka/pull/13312#issuecomment-1448299260

   > It is interesting that unrolling the loop while keeping the same underlying logic yields this increase in throughput for writing varints
   
   Yes, indeed. In non hotspot code paths, which would be over-optimization and we may just want to leave it to the compiler to perform unrolling. But in hot code paths such as this PR, manual changes could lead to faster execution of cases where the compiler is not smart enough.
   
   As example of a prior change of similar nature, see: https://github.com/apache/kafka/pull/11721 (that PR claims to improve CPU by 6% in a real workload)
   
   > What CPU architectures have this been tested on?
   
   The processor architecture for the above numbers is `Intel(R) Xeon(R) Platinum 8175M CPU @ 2.50GHz`. I have also added number for ARM now.
   
   > Do we have any data on how these gains translate in latency reduction with real requests from canonical workloads?
   
   I haven't performed that benchmark right now. I believe that the JMH benchmark gains should be good enough justification to merge this change. But as an aside, yes, I do plan to benchmark latency reduction later when my other performance related PRs (there are some compression ones open) have also been merged.


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