On 12.10.2011, at 22:41, Stefan Weil wrote: > Am 12.10.2011 22:02, schrieb Alexander Graf: >> Actually, I'd much rather prefer to keep the differences between KVM and >> non-KVM low here. THP can potentially also work on TCG, so the alignment >> isn't completely moot here. Though it's certainly a lot less useful, as code >> isn't directly executed from there and we the rest of the overhead is a lot >> higher either way (especially the softmmu one). >> Either way, why does valgrind break when we enforce big alignment? That >> really sounds more like a valgrind bug than anything else. Memalign is there >> for exactly that reason, no? >> >> >> Alex > > Actually, there is even a difference between KVM (x86_64) and KVM (non x86_64) > in the current code: only x86_64 hosts use the 2 MiB alignment.
Right. It might make sense to find a reasonable alignment for all archs and just set it to that. I vote for 16MB :). > Valgrind breaks because it has an assertion which limits the alignment. > This limitation was already discussed in 2008 and still exists in latest > Ubuntu and other distributions (and also in latest Valgrind SVN trunk). > > Therefore I don't expect that it will be fixed soon. > > See these bug reports, for example: > > http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=489297 > http://bugs.kde.org/show_bug.cgi?id=203877 Well, yes, my point is that it's a bug in valgrind that should be fixed. I don't think we should special-case QEMU because of bugs in debugging software :) Alex
