[lkml]   [2018]   [Feb]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v2 1/3] x86/entry: Clear extra registers beyond syscall arguments for 64bit kernels
On Mon, Feb 5, 2018 at 2:22 PM, Linus Torvalds
<> wrote:
> But I'm not timing it.

I lied.

I did this:

for (i = 0; i < 100000; i++)
asm(".rept 16384\n"
"subq $128,%rsp\n\t"
"pushq %rbx\n\t"
"pushq %r10\n\t"
"pushq %r11\n\t"
"pushq %r12\n\t"
"pushq %r13\n\t"
"pushq %r14\n\t"
"pushq %r15\n\t"

"popq %r15\n\t"
"popq %r14\n\t"
"popq %r13\n\t"
"popq %r12\n\t"
"popq %r11\n\t"
"popq %r10\n\t"
"popq %rbx\n\t"
"addq $128,%rsp\n\t"

and then I timed it like that, and with "xorq" of the register after
each "pushq".

And the timings came out the same, to within the (bad) timing I did.

So I really do think you can just put the xor right next to the push,
and it will be effectively free.


 \ /
  Last update: 2018-02-05 23:26    [W:0.072 / U:0.520 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site