From d860d40327dde251d508a234fa00bd0d90fbb656 Mon Sep 17 00:00:00 2001 From: Shan Wei Date: Thu, 19 Jun 2014 14:12:44 -0700 Subject: [PATCH] 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 Acked-by: Christoph Lameter Signed-off-by: Pranith Kumar Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett Reviewed-by: Lai Jiangshan --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 8f3e4d43d736..a6c5424ffa38 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2487,7 +2487,7 @@ static void force_quiescent_state(struct rcu_state *rsp) struct rcu_node *rnp_old = NULL; /* Funnel through hierarchy to reduce memory contention. */ - rnp = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode; + rnp = __this_cpu_read(rsp->rda->mynode); for (; rnp != NULL; rnp = rnp->parent) { ret = (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) || !raw_spin_trylock(&rnp->fqslock);