Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753062AbaGGWjq (ORCPT ); Mon, 7 Jul 2014 18:39:46 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:38247 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752722AbaGGWid (ORCPT ); Mon, 7 Jul 2014 18:38:33 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, sbw@mit.edu, "Paul E. McKenney" , Shan Wei , Pranith Kumar Subject: [PATCH tip/core/rcu 13/17] rcu: Use __this_cpu_read() instead of per_cpu_ptr() Date: Mon, 7 Jul 2014 15:38:17 -0700 Message-Id: <1404772701-8804-13-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1404772701-8804-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20140707223756.GA7187@linux.vnet.ibm.com> <1404772701-8804-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14070722-3532-0000-0000-000002FA8B93 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" 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 --- 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); -- 1.8.1.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/