On Wed, 19 Dec 2018, Li, Aubrey wrote: > On 2018/12/19 5:38, 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. > > > > Other alternative would be to use 32bit jiffies on 32bit. I assume > > wrapping is not that big a problem here. > > > Thomas, is this acceptable?
Just do the math. jiffies on 32bit wrap around depending on HZ: HZ=100 248 days HZ=1000 24 days So, yes it takes quite some time, but from then on the information is bogus. Whether that matters or not is a different question. At least it needs proper documentation. Thanks, tglx