* Dave Hansen <dave.hansen@xxxxxxxxx> wrote: > On 3/5/25 01:07, Ingo Molnar wrote:>> Alternatives considered: > >> - Make kernel-mode FPU sections fully preemptible. This would require > >> growing task_struct by another struct fpstate which is more than 2K. > > > > So that's something that will probably happen once the kernel is built > > using APX anyway? > > I was expecting that building the kernel with APX would be very > different than a kernel_fpu_begin(). We don't just need *one* more > save area for APX registers: we need a stack, just like normal GPRs. Yes - but my point is: with any APX build we'd probably be saving FPU(-ish) registers at entry points, into a separate context area. If that includes FPU registers then we'd not have to do kernel_fpu_begin()/end(). In other words, we'd be doing something close to 'growing task_struct by another struct fpstate', or so - regardless of whether it's in task_struct or some sort of extended pt_regs. The kernel would also be close to 'FPU-safe', i.e. there likely wouldn't be a need for kernel_fpu_begin()/end(). Thanks, Ingo
