I would also like to mention that your code assumes 64-bit atomics support which we don't have on 32-bit systems. Using 32-bit to track ASID generations isn't sufficient and will cause overflows. That's why I have asid_generation_overflow to handle the case (this is super error-prone as well).
Best, Gary On 27/03/2019 11:42, Anup Patel wrote: > On Wed, Mar 27, 2019 at 4:57 PM Gary Guo <g...@garyguo.net> wrote: >> >> Hi Anup, >> >> This won't work in an actual hardware with ASID support. There're more > > Can you elaborate why? > > This implementation is based on Linux ARM64 ASID allocator which is > tested for large number of CPUs on real HW. > >> interactions with TLB flushes that need to be considered. You won't see > > Yap, already considered. Please point me to unhandled case. > >> this on both QEMU and SiFive board, as QEMU does not have ASID, so it >> pretends that ASID is supported by just flushing its TLB everytime you > > Nope, it does not. It detects whether ASID is supported or not. If supported > it will also figure-out number of ASID bits supported by HW. > > SiFive board does not have ASID bits so this implementation successfully > detects that number of ASID bits are 0 and fallbacks to original way of > local TLB flushes. > >> change sptbr. I suspect the performance gain you see is just due to >> saved TLB flush as TLB flush is super expensive in QEMU (all translation >> block jumps need to be cleared). > > Yes, performance gain is due to saved TLB flushes. > > On HW which supports ASID bits, we will see more performance > improvements. > >> >> I have my version here https://github.com/nbdd0121/linux/tree/asid. I >> haven't done code cleanups yet, but this version has correctness of its >> ASID code tested on our TLB simulator tool (which unfortunately I can't >> share right now as it involves with unpublished works). > > Except few minor differences. You version of ASID allocator is same as > mine. In fact there are lot of similar code framgements in your version > compared to Linux ARM64 as well. I am sure this patch will work for you. > >> >> In fact my submit my previous patch series exactly as the basis of this >> patch. > > This patch is based your patch series so I suggest you take this patch > and try it on your simulator. > > Suggestions and improvements to this patch are welcomed. > > I would be happy if you can assist me to try on your HW. > > Regards, > Anup >
