Messages in this thread | | | Date | Sat, 12 Mar 2016 16:45:02 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs |
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* Denys Vlasenko <dvlasenk@redhat.com> wrote:
> Use of a temporary R8 register here seems to be unnecessary. > > "push %r8" is a two-byte insn (it needs REX prefix to specify R8), > "push $0" is two-byte too. It seems just using the latter would be > no worse. > > Thus, code had an unnecessary "xorq %r8,%r8" insn. > It probably costs nothing in execution time here since we are probably > limited by store bandwidth at this point, but still.
Note that the 3 fewer instruction in the image also shrink the code by 16 bytes:
arch/x86/entry/entry_64_compat.o:
text data bss dec hex filename 380 0 0 380 17c entry_64_compat.o.before 364 0 0 364 16c entry_64_compat.o.after
because (at least in this defconfig build) one of these functions shrunk below a 16-byte boundary. So cache footprint got denser.
Thanks,
Ingo
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