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

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

[Shan Wei]

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(-)

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

[Christoph Lameter]

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.