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SubjectRe: [PATCH 0/9 v2] use efficient this_cpu_* helper
On Sat, 3 Nov 2012, Shan Wei wrote:

> this_cpu_ptr is faster than per_cpu_ptr(p, smp_processor_id())
> and can reduce memory accesses.
> The latter helper needs to find the offset for current cpu,
> and needs more assembler instructions which objdump shows in following.
>
> per_cpu_ptr(p, smp_processor_id()):
> 1e: 65 8b 04 25 00 00 00 00 mov %gs:0x0,%eax
> 26: 48 98 cltq
> 28: 31 f6 xor %esi,%esi
> 2a: 48 c7 c7 00 00 00 00 mov $0x0,%rdi
> 31: 48 8b 04 c5 00 00 00 00 mov 0x0(,%rax,8),%rax
> 39: c7 44 10 04 14 00 00 00 movl $0x14,0x4(%rax,%rdx,1)
>
> this_cpu_ptr(p)
> 1e: 65 48 03 14 25 00 00 00 00 add %gs:0x0,%rdx
> 27: 31 f6 xor %esi,%esi
> 29: c7 42 04 14 00 00 00 movl $0x14,0x4(%rdx)
> 30: 48 c7 c7 00 00 00 00 mov $0x0,%rdi

this_cpu_read() etc even avoids the use of this_cpu_ptr()
reducing the 6 instructions earlier to 1.
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