A performance regression

So, another day at the customer site, another issue to fix:

Issue 234. Over the past three months, the performance of [PRODUCT] has regressed. In December, at commit 919074d, [TESTCASE] ran in 21 seconds, but now it takes 44 seconds.

The first step is to check that the problem is reproducible (it is), ( and the next is to run a git bisect to see if there was a bad commit … )