On Mon, 16 Jun 2014 20:21:20 -0400 Steven Rostedt <rost...@goodmis.org> wrote:
> On Mon, 16 Jun 2014 16:54:32 -0700 (PDT) > David Rientjes <rient...@google.com> wrote: > > > > > > > On linux-next, allyesconfig has a 0.0001% savings as a result of the > > patch, but I'd be worried about the extra temp variable it allocates on > > the stack that is evident in the mm/slab.c disassembly unless all cases > > can be audited to show that we're not potentially deep. > > A 0.0001% change means it's not worth changing, and we may be able to > mark this up as a fluke in Michal's results. > > I'll give it a try on my 4.6.3 compiler. > > -- Steve > > > > > text data bss dec hex filename > > 108573045 23488016 51580928 183641989 af22785 > > vmlinux.before > > 108572908 23488016 51580928 183641852 af226fc > > vmlinux.after > Here's my results: text data bss dec hex filename 108662851 23470256 51580928 183714035 af340f3 /tmp/vmlinux-orig 108662714 23470224 51580928 183713866 af3404a /tmp/vmlinux-patched The patched version saved a total of 169 bytes. Doing a diff on the vmlinux objdumps of do_fault_around, I get this: mov -0x68(%rbp),%rdi mov -0x70(%rbp),%r8d - jae ffffffff81302bf5 <do_fault_around+0xbd> - cmp %r15,%rax - mov %r15,%r14 - cmovbe %rax,%r14 - jmp ffffffff81302c03 <do_fault_around+0xcb> - cmp %r14,%rax - cmovbe %rax,%r14 - incq 0x8d384b5(%rip) # ffffffff8a03b0b8 <high_memory+0x14e8> - mov 0x8d384be(%rip),%rsi # ffffffff8a03b0c8 <high_memory+0x14f8> - mov 0x8d384bf(%rip),%rdx # ffffffff8a03b0d0 <high_memory+0x1500> - mov 0x8d384a8(%rip),%rax # ffffffff8a03b0c0 <high_memory+0x14f0> + cmp %rax,%r15 + cmova %rax,%r15 + mov 0x8d384c0(%rip),%rax # ffffffff8a03b0b8 <high_memory+0x14e8> + cmp %r14,%r15 + cmovbe %r15,%r14 sub %r12,%rsi So for gcc 4.6.3 it does seem to produce nicer assembly. I haven't tried it with other versions though (or with clang). But I'll still give it a: Acked-by: Steven Rostedt <rost...@goodmis.org> -- Steve -- 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/
