Hi Song, On Fri, May 20, 2022 at 04:57:50PM -0700, Song Liu wrote: ... ... > The primary goal of bpf_prog_pack is to reduce iTLB miss rate and reduce > direct memory mapping fragmentation. This leads to non-trivial performance > improvements. > > For our web service production benchmark, bpf_prog_pack on 4kB pages > gives 0.5% to 0.7% more throughput than not using bpf_prog_pack. > bpf_prog_pack on 2MB pages 0.6% to 0.9% more throughput than not using > bpf_prog_pack. Note that 0.5% is a huge improvement for our fleet. I > believe this is also significant for other companies with many thousand > servers. > I'm evaluationg performance impact due to direct memory mapping fragmentation and seeing the above, I wonder: is the performance improve mostly due to prog pack and hugepage instead of less direct mapping fragmentation? I can understand that when progs are packed together, iTLB miss rate will be reduced and thus, performance can be improved. But I don't see immediately how direct mapping fragmentation can impact performance since the bpf code are running from the module alias addresses, not the direct mapping addresses IIUC? I appreciate it if you can shed some light on performance impact direct mapping fragmentation can cause, thanks.
