this_cpu_ptr is faster than per_cpu_ptr(p, smp_processor_id()).
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
$ git diff --stat a932657f51eadb8280166e82dc7034dfbff3985a..
drivers/clocksource/arm_generic.c | 2 +-
include/trace/ftrace.h | 4 +---
kernel/padata.c | 2 +-
kernel/rcutree.c | 2 +-
kernel/trace/blktrace.c | 2 +-
kernel/trace/trace.c | 2 +-
net/core/flow.c | 4 +---
net/openvswitch/datapath.c | 4 ++--
net/openvswitch/vport.c | 5 ++---
net/rds/ib_recv.c | 2 +-
net/xfrm/xfrm_ipcomp.c | 7 +++----
11 files changed, 15 insertions(+), 21 deletions(-)
On Wed, 31 Oct 2012, Shan Wei wrote:
> this_cpu_ptr is faster than per_cpu_ptr(p, smp_processor_id()).
> The latter helper needs to find the offset for current cpu,
> and needs more assembler instructions which objdump shows in following.
The code is shorter and that helps but note that the main effect is that
memory accesses are reduced.