On Thu, Feb 5, 2015 at 5:52 PM, Richard Henderson <r...@twiddle.net> wrote: > On 02/04/2015 09:09 PM, Patrick Williams III wrote: >>>I think one possible way is to clear the software tlb on entry to the >>>transaction and disable (not install any translations) the software >>>TLB till the end of the transaction. >>>In the softmmu helper functions, the memory addresses as well as >>>value can then be tracked in a hashtable and committed to system >>>memory once the transaction is ready to be committed. >> >> I believe the transaction conflicts are handled post-translation by the cache >> coherency protocol. Trying to store the pre-translation address isn't >> sufficient for conflict resolution. >> >> Consider two virtual addresses that point to the same physical address. One >> thread uses the first virtual address in a transaction; another thread writes >> to the second virtual address while the transaction is going on. This should >> cause the transaction to fail because the same physical address was involved. > > That's not really relevant. The important part is that no TLB hits are made > within TCG, so that we always use the softmmu helpers. > > Incidentally, that's also accomplished by bits such as TLB_NOTDIRTY. We could > add another bit so that pages referenced by TM don't need to be fetched out of > the page tables every time. > > > r~
I agree conflict detection should be down on physical addresses. we do have physical addresses in the softmmu helpers. On a side note, is there a plan to be provide a set of functionalities in QEMU to make implementing transactional memory easier ? Xin
