On Tue, Dec 18, 2018 at 01:44:41PM -0800, Dave Hansen wrote: > On 12/18/18 1:38 PM, Andi Kleen wrote: > >> I misunderstood, you mean 32bit kernel, not 32bit machine. Theoretically > >> 32bit > >> kernel can use AVX512, but not sure if anyone use it like this. > >> get_jiffies_64() > >> includes jiffies_lock ops so not good in context switch. So I want to use > >> raw > >> jiffies_64 here. jiffies is a good candidate but it has wraparound > >> overflow issue. > >> Other time source are expensive here. > >> > >> Should I limit the code only running on 64bit kernel? > > Yes making it 64bit only should be fine. > > I think I'd rather just disable AVX512 itself on 32-bit and be done with > it. I think more than half of the ~2k of XSAVE space that it consumes > in *every* *task* is just pure waste because it has to be 0's. > > This ~2k of extra space is also lowmem, which makes it even more valuable.
That will actually break programs. If someone compiled binaries with -march=native on a system with AVX512 they wouldn't work anymore. Don't think we can do it. -Andi
