Linux 6.15 Git Tanked Nginx HTTPS Web Server Performance - Here's The Bisect
First up on this AMD EPYC 9655P server I repeated the tests of Linux 6.14 and Linux 6.15 Git as of earlier today while building from source rather than the Ubuntu Mainline Kernel PPA.
Indeed, with these fresh kernel builds locally confirming what I saw out of the Ubuntu Mainline Kernel PPA kernels... The throughput of Nginx absolutely tanked on this Linux server using the in-development v6.15 kernel. With this additional testing, for good measure I also used two different sizes for this single-server benchmark configuration of the Nginx web server in HTTPS configuration and using wrk as the on-server load generator for benchmarking of the throughput for serving a simple static HTML web page.
Thanks to being able to reproduce the kernel regression on the high core count 5th Gen AMD EPYC server and the Nginx+Wrk benchmark not being too long, it was a quick and justifiable bisect:
A few hours later, it was tracked down to a recent post-merge-window commit: locking/local_lock, mm: replace localtry_ helpers with local_trylock_t type.
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Now to look at the Linux 6.15 performance on some additional systems and seeing if some of the other regressed workloads can be attributed to this same commit.
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