From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755486Ab3AHWdP (ORCPT ); Tue, 8 Jan 2013 17:33:15 -0500 Received: from mx1.redhat.com ([209.132.183.28]:18436 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754097Ab3AHWdO (ORCPT ); Tue, 8 Jan 2013 17:33:14 -0500 Date: Tue, 8 Jan 2013 17:32:52 -0500 From: Rik van Riel To: linux-kernel@vger.kernel.org Cc: aquini@redhat.com, walken@google.com, eric.dumazet@gmail.com, lwoodman@redhat.com, jeremy@goop.org, Jan Beulich , knoel@redhat.com, chegu_vinod@hp.com, raghavendra.kt@linux.vnet.ibm.com, mingo@redhat.com Subject: [PATCH 1/5] x86,smp: move waiting on contended ticket lock out of line Message-ID: <20130108173252.02a42e89@annuminas.surriel.com> In-Reply-To: <20130108172632.1126898a@annuminas.surriel.com> References: <20130108172632.1126898a@annuminas.surriel.com> Organization: Red Hat, Inc. Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Moving the wait loop for congested loops to its own function allows us to add things to that wait loop, without growing the size of the kernel text appreciably. Signed-off-by: Rik van Riel Reviewed-by: Steven Rostedt Reviewed-by: Michel Lespinasse Reviewed-by: Rafael Aquini --- v2: clean up the code a little, after Michel's suggestion arch/x86/include/asm/spinlock.h | 11 +++++------ arch/x86/kernel/smp.c | 14 ++++++++++++++ 2 files changed, 19 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h index 33692ea..dc492f6 100644 --- a/arch/x86/include/asm/spinlock.h +++ b/arch/x86/include/asm/spinlock.h @@ -34,6 +34,8 @@ # define UNLOCK_LOCK_PREFIX #endif +extern void ticket_spin_lock_wait(arch_spinlock_t *, struct __raw_tickets); + /* * Ticket locks are conceptually two parts, one indicating the current head of * the queue, and the other indicating the current tail. The lock is acquired @@ -53,12 +55,9 @@ static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock) inc = xadd(&lock->tickets, inc); - for (;;) { - if (inc.head == inc.tail) - break; - cpu_relax(); - inc.head = ACCESS_ONCE(lock->tickets.head); - } + if (inc.head != inc.tail) + ticket_spin_lock_wait(lock, inc); + barrier(); /* make sure nothing creeps before the lock is taken */ } diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c index 48d2b7d..20da354 100644 --- a/arch/x86/kernel/smp.c +++ b/arch/x86/kernel/smp.c @@ -113,6 +113,20 @@ static atomic_t stopping_cpu = ATOMIC_INIT(-1); static bool smp_no_nmi_ipi = false; /* + * Wait on a congested ticket spinlock. + */ +void ticket_spin_lock_wait(arch_spinlock_t *lock, struct __raw_tickets inc) +{ + for (;;) { + cpu_relax(); + inc.head = ACCESS_ONCE(lock->tickets.head); + + if (inc.head == inc.tail) + break; + } +} + +/* * this function sends a 'reschedule' IPI to another CPU. * it goes straight through and wastes no time serializing * anything. Worst case is that we lose a reschedule ...