rcu: Use __this_cpu_read() instead of per_cpu_ptr()
The __this_cpu_read() function produces better code than does
per_cpu_ptr() on both ARM and x86. For example, gcc (Ubuntu/Linaro
4.7.3-12ubuntu1) 4.7.3 produces the following:
ARMv7 per_cpu_ptr():
force_quiescent_state:
mov r3, sp @,
bic r1, r3, #8128 @ tmp171,,
ldr r2, .L98 @ tmp169,
bic r1, r1, #63 @ tmp170, tmp171,
ldr r3, [r0, #220] @ __ptr, rsp_6(D)->rda
ldr r1, [r1, #20] @ D.35903_68->cpu, D.35903_68->cpu
mov r6, r0 @ rsp, rsp
ldr r2, [r2, r1, asl #2] @ tmp173, __per_cpu_offset
add r3, r3, r2 @ tmp175, __ptr, tmp173
ldr r5, [r3, #12] @ rnp_old, D.29162_13->mynode
ARMv7 __this_cpu_read():
force_quiescent_state:
ldr r3, [r0, #220] @ rsp_7(D)->rda, rsp_7(D)->rda
mov r6, r0 @ rsp, rsp
add r3, r3, #12 @ __ptr, rsp_7(D)->rda,
ldr r5, [r2, r3] @ rnp_old, *D.29176_13
Using gcc 4.8.2:
x86_64 per_cpu_ptr():
movl %gs:cpu_number,%edx # cpu_number, pscr_ret__
movslq %edx, %rdx # pscr_ret__, pscr_ret__
movq __per_cpu_offset(,%rdx,8), %rdx # __per_cpu_offset, tmp93
movq %rdi, %r13 # rsp, rsp
movq 1000(%rdi), %rax # rsp_9(D)->rda, __ptr
movq 24(%rdx,%rax), %r12 # _15->mynode, rnp_old
x86_64 __this_cpu_read():
movq %rdi, %r13 # rsp, rsp
movq 1000(%rdi), %rax # rsp_9(D)->rda, rsp_9(D)->rda
movq %gs:24(%rax),%r12 # _10->mynode, rnp_old
Because this change produces significant benefits for these two very
diverse architectures, this commit makes this change.
Signed-off-by: Shan Wei <davidshan@tencent.com>
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
d860d40327