[PATCH 0/9] use this_cpu_ptr instead of per_cpu_ptr(p, smp_processor_id())

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.