On Fri, Dec 18, 2020 at 06:01:01PM +0100, Ard Biesheuvel wrote: > [ TL;DR for the non-ARM folks on CC: disabling softirq processing when using > SIMD in kernel mode could reduce complexity and improve performance, but we > need to decide whether we can do this, and how much softirq processing > latency we can tolerate. If we can find a satisfactory solution for this, > we might do the same for x86 and 32-bit ARM as well. ]
> - could we do the same on x86, now that kernel_fpu_begin/end is no longer > expensive? Can't we simply save/restore the relevant register set? So something like (note amluto was wanting to add a regset argument): <task> kernel_fpu_begin(MMX) <SIRQ> kernel_fpu_begin(SSE) kernel_fpu_end(); </SIRQ> ... kernel_fpu_end() Would have to save the MMX regs on first SIRQ invocation of kernel_fpu_begin(), and then have softirq context termination </SIRQ> above, restore it. I mean, we already do much the same for the first kernel_fpu_begin(), that has to save the user registers, which will be restore when we go back to userspace. So why not do exactly the same for softirq context?