Joel Stanley <j...@jms.id.au> writes: > On Thu, 24 Aug 2023 at 12:12, Michael Ellerman <m...@ellerman.id.au> wrote: >> >> Michael Ellerman <m...@ellerman.id.au> writes: >> > Michael Ellerman <m...@ellerman.id.au> writes: >> >> "Nicholas Piggin" <npig...@gmail.com> writes: >> >>> On Wed Jun 14, 2023 at 3:56 PM AEST, Michael Ellerman wrote: >> >>>> Michael Ellerman <m...@ellerman.id.au> writes: >> >>>> > Nicholas Piggin <npig...@gmail.com> writes: >> >>>> >> The most expensive ordering for hwsync to provide is the store-load >> >>>> >> barrier, because all prior stores have to be drained to the caches >> >>>> >> before subsequent instructions can complete. >> >>>> >> >> >>>> >> stsync just orders stores which means it can just be a barrer that >> >>>> >> goes down the store queue and orders draining, and does not prevent >> >>>> >> completion of subsequent instructions. So it should be faster than >> >>>> >> hwsync. >> >>>> >> >> >>>> >> Use stsync for wmb(). Older processors that don't recognise the SC >> >>>> >> field should treat this as hwsync. >> >>>> > >> >>>> > qemu (7.1) emulating ppc64e does not :/ >> >>>> > >> >>>> > mpic: Setting up MPIC " OpenPIC " version 1.2 at fe0040000, max 1 >> >>>> > CPUs >> >>>> > mpic: ISU size: 256, shift: 8, mask: ff >> >>>> > mpic: Initializing for 256 sources >> >>>> > Oops: Exception in kernel mode, sig: 4 [#1] >> >>>> .. >> >>>> > >> >>>> > I guess just put it behind an #ifdef 64S. >> >>>> >> >>>> That doesn't work because qemu emulating a G5 also doesn't accept it. >> >>>> >> >>>> So either we need to get qemu updated and wait a while for that to >> >>>> percolate, or do some runtime patching of wmbs in the kernel >_< >> >>> >> >>> Gah, sorry. QEMU really should be ignoring reserved fields in >> >>> instructions :( >> >> >> >> Yeah, it's an annoying discrepancy vs real hardware and the ISA. >> >> >> >>> I guess leave it out for now. Should fix QEMU but we probably also need >> >>> to do patching so as not to break older QEMUs. >> >> >> >> I'll plan to take the first 3 patches, they seem OK as-is. >> > >> > I didn't do that in the end, because patch 2 suffers from the same >> ^ >> 3 >> > problem of not working on QEMU. > > Did we get a patch to fix this in to Qemu?
No. Nick might have looked at it but he hasn't posted anything AFAIK. cheers
