Hi, On 2023-10-08 06:20, Johannes Schauer Marin Rodrigues wrote: > I'm wondering whether it'd make sense for the Debian kernel to be built with > CONFIG_PREEMPT_DYNAMIC=y.
On amd64 we already have PREEMPT_DYNAMIC=y, so I thought of running some benchmarks on my Ryzen system to evaluate the performance overhead it introduces. To my surprise, I found that in Debian you get a 20% (!) performance improvement on kernel-heavy workloads simply by setting PREEMPT_DYNAMIC to 'n'. I brought up the topic on LKML [1], and it turns out that what is really eating performance for us is DEBUG_PREEMPT=y. There is a performance penalty in PREEMPT_DYNAMIC=y as well, but it's much smaller, around 3 or 4%. The Kconfig help entry for DEBUG_PREEMPT also clearly mentions the performance overhead: This option has potential to introduce high runtime overhead, depending on workload as it triggers debugging routines for each this_cpu operation. It should only be used for debugging purposes. Regardless of what we are going to decide about PREEMPT_DYNAMIC, we surely have to disable DEBUG_PREEMPT. I opened [2] for that. [1] https://lore.kernel.org/lkml/ZTJFA_Ac6nWawIHb@ariel/ [2] https://salsa.debian.org/kernel-team/linux/-/merge_requests/874
