jvq 0.6 Counts Instructions Under Valgrind to Catch a 2 Percent Slowdown on a Noisy Runner

Mon, 19 Oct 2026 00:00:00 +0000

Time is a noisy thing to gate on. On our 2-core test machine the same benchmark spreads 7 to 9% from run to run, so jvq’s default budget is 5%, and a 2% slowdown walks straight through. It should, given the noise. But 2% is real, and a dozen of them add up.

Version 0.6 has a second way to measure. The instructions adapter runs the benchmark under valgrind’s cachegrind and counts every instruction it executes. A count doesn’t care how busy the machine is. Run the same program twice and you get nearly the same number, so the budget can drop to 1%.

Linux on JVQ.net

jvq 0.6 Counts Instructions Under Valgrind to Catch a 2 Percent Slowdown on a Noisy Runner