* Denys Vlasenko <dvlas...@redhat.com> wrote: > > The decision on how exactly we should fix > > KERNEL_STACK_OFFSET (set it to SIZEOF_PTREGS or to > > zero) depends on whether we switch to using PUSHes, or > > not. What do you think?
Yes. > A data point. I implemented push-based creation of > pt_regs and benchmarked it. The patch is on top of all my > latest patches sent to ML. > > On SandyBridge CPU, it does not get slower: seems to be 1 > cycle faster per syscall. > > We lose a number of large insns there: > > text data bss dec hex filename > - 9863 0 0 9863 2687 entry_64.o > + 9671 0 0 9671 25c7 entry_64.o That's a nice reduction in I$ footprint ... > + /* Construct struct pt_regs on stack */ > + pushq $__USER_DS /* pt_regs->ss */ > + pushq PER_CPU_VAR(old_rsp) /* pt_regs->sp */ > + pushq %r11 /* pt_regs->flags */ Btw., this could also construct all the dwarf annotations in a natural, maintainable fashion - pushq_cfi and friends? > + pushq $__USER_CS /* pt_regs->cs */ > + pushq %rcx /* pt_regs->ip */ > + pushq %rax /* pt_regs->orig_ax */ > + pushq %rdi /* pt_regs->di */ > + pushq %rsi /* pt_regs->si */ > + pushq %rdx /* pt_regs->dx */ > + pushq %rcx /* pt_regs->cx */ > + pushq $-ENOSYS /* pt_regs->ax */ > + pushq %r8 /* pt_regs->r8 */ > + pushq %r9 /* pt_regs->r9 */ > + pushq %r10 /* pt_regs->r10 */ > + sub $(7*8),%rsp /* pt_regs->r11,bp,bx,r12-15 */ So the 'SUB' there is a bit sad, but push sequences are generally easier to read, so I like it altogether. Then we could indeed get rid of KERNEL_STACK_OFFSET. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/