I worked with https://github.com/SUSE/kernel. I checked out v5.8 and 5.9 and compiled. Both kernels were preempt kernels and showed the speed regression against "Linux hertz 5.3.18-lp152.78-preempt #1 SMP PREEMP". I had tested before against home:tiwai:kernel:5.9 and home:tiwai:kernel:5.8 and had the speed regression. I am confused now.