On Wed, Aug 2, 2023 at 10:52 PM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote: > > 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. Will do. Thanks, Saravana
