On 2019-04-12 19:29:31 [+0200], Borislav Petkov wrote: > > - in kernel_fpu_begin() we may trash the task's FPU state (by saving its > > registers or by resetting fpu_fpregs_owner_ctx). > > Do we care? > > You mean, in case you have workloads which might involve a lot of > in-kernel FPU use which would punish task context switches? Well, depends how you look on it. So for instance: - Does kernel_fpu_begin() save task's FPU registers or are they already stored and it is a nop. - The task avoid loading its registers on return to userland but that FPU usage in BH made it impossible. - Is there any FPU usage in BH? And there is this: My program usually works but with this scheduling pattern and FPU usage in kernel it computes wrong result. Sebastian
