On Wed, 2013-08-21 at 10:14 -0700, Andi Kleen wrote: > Torvald Riegel <trie...@redhat.com> writes: > > +#endif > > leaq 8(%rsp), %rax > > - subq $56, %rsp > > - cfi_def_cfa_offset(64) > > + subq $64, %rsp > > + cfi_def_cfa_offset(72) > > I don't see why you did this change and the addq change below.
I need to store edi (ie, the properties of the transaction passed to the function by the compiler) on the stack, so these two changes create additional room for it. (I wasn't sure about alignment requirements, so I just used 8 bytes for it.) > The rest seems reasonable to me, although I haven't tried to untangle > the full dependencies between C++ and asm code for retries. If anyone has any suggestions for how to improve the comments, let me know. > It would be likely cleaner to just keep the retries fully > in C++ like the original patch did. There's no advantage > of going back to assembler. That's true for x86, but it seems that for s390, we can't easily put the xbegin/tbegin into the C++ code because of floating point register save/restore issues. The added complexity on the x86 side seemed to be a reasonable price for having a general HTM fast path retry handling on the C++ side. Torvald
