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SubjectRe: [PATCH 00/10] jump label: introduce very_[un]likely + cleanups + docs
On Thu, Feb 23, 2012 at 11:33:48PM +0100, Ingo Molnar wrote:
>
> Before:
>
> ffffffff810441f0 <sys_getppid>:
> ffffffff810441f0: 8b 05 8a 52 d8 00 mov 0xd8528a(%rip),%eax # ffffffff81dc9480 <key>
> ffffffff810441f6: 55 push %rbp
> ffffffff810441f7: 48 89 e5 mov %rsp,%rbp
> ffffffff810441fa: 85 c0 test %eax,%eax
> ffffffff810441fc: 75 27 jne ffffffff81044225 <sys_getppid+0x35>
> ffffffff810441fe: 65 48 8b 04 25 c0 b6 mov %gs:0xb6c0,%rax
> ffffffff81044205: 00 00
> ffffffff81044207: 48 8b 80 80 02 00 00 mov 0x280(%rax),%rax
> ffffffff8104420e: 48 8b 80 b0 02 00 00 mov 0x2b0(%rax),%rax
> ffffffff81044215: 48 8b b8 e8 02 00 00 mov 0x2e8(%rax),%rdi
> ffffffff8104421c: e8 2f da 00 00 callq ffffffff81051c50 <pid_vnr>
> ffffffff81044221: 5d pop %rbp
> ffffffff81044222: 48 98 cltq
> ffffffff81044224: c3 retq
> ffffffff81044225: 48 c7 c7 13 53 98 81 mov $0xffffffff81985313,%rdi
> ffffffff8104422c: 31 c0 xor %eax,%eax
> ffffffff8104422e: e8 60 0f 6d 00 callq ffffffff81715193 <printk>
> ffffffff81044233: eb c9 jmp ffffffff810441fe <sys_getppid+0xe>
> ffffffff81044235: 66 66 2e 0f 1f 84 00 data32 nopw %cs:0x0(%rax,%rax,1)
> ffffffff8104423c: 00 00 00 00
>
> After:
>
> ffffffff81044290 <sys_getppid>:
> ffffffff81044290: 55 push %rbp
> ffffffff81044291: 48 89 e5 mov %rsp,%rbp
> ffffffff81044294: e9 00 00 00 00 jmpq ffffffff81044299 <sys_getppid+0x9>
> ffffffff81044299: 65 48 8b 04 25 c0 b6 mov %gs:0xb6c0,%rax
> ffffffff810442a0: 00 00
> ffffffff810442a2: 48 8b 80 80 02 00 00 mov 0x280(%rax),%rax
> ffffffff810442a9: 48 8b 80 b0 02 00 00 mov 0x2b0(%rax),%rax
> ffffffff810442b0: 48 8b b8 e8 02 00 00 mov 0x2e8(%rax),%rdi
> ffffffff810442b7: e8 f4 d9 00 00 callq ffffffff81051cb0 <pid_vnr>
> ffffffff810442bc: 5d pop %rbp
> ffffffff810442bd: 48 98 cltq
> ffffffff810442bf: c3 retq
> ffffffff810442c0: 48 c7 c7 e3 54 98 81 mov $0xffffffff819854e3,%rdi
> ffffffff810442c7: 31 c0 xor %eax,%eax
> ffffffff810442c9: e8 71 13 6d 00 callq ffffffff8171563f <printk>
> ffffffff810442ce: eb c9 jmp ffffffff81044299 <sys_getppid+0x9>
>
> The prior slowpath test:
>
> ffffffff810441fa: 85 c0 test %eax,%eax
> ffffffff810441fc: 75 27 jne ffffffff81044225 <sys_getppid+0x35>
>
> became even faster and turned into a single NOP, making the
> fastpath even faster.
>

and the: mov 0xd8528a(%rip),%eax # ffffffff81dc9480 <key>

is no longer present.

Thanks,

-Jason


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