On 02-08-23, 15:16, Saravana Kannan wrote: > This is mainly an optimization to reduce the latency of the "frequency > change" which has a huge impact on the performance (as can be seen > from the numbers in the cover letter). > > Setting this flag means that the vCPU thread triggering the MMIO > handling (on the host side) is the thread on which the host needs to > apply any uclamp settings. So this avoids the VMM having to look up > the right vCPU thread that corresponds to this CPU, and any > permissions issues wrt setting another threads uclamp, etc. This > becomes even more important if/when BPF support is added for handling > simple MMIO read/writes. Will Deacon has been working on the eBPF > part[1] and IIUC, not setting this flag adds a lot of extra overhead > on the BPF side. > > So, yeah, this flag is very helpful wrt reducing latency/simplifying > host side implementation and that's why we want it here. > > [1] - https://kvm-forum.qemu.org/2023/talk/AZKC77/ Would be good to have a (big) comment in the code explaining that as it isn't obvious. Thanks. -- viresh
