From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760193AbdACSCJ (ORCPT ); Tue, 3 Jan 2017 13:02:09 -0500 Received: from mx1.redhat.com ([209.132.183.28]:42134 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760101AbdACSBR (ORCPT ); Tue, 3 Jan 2017 13:01:17 -0500 From: Waiman Long To: Peter Zijlstra , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" Cc: linux-kernel@vger.kernel.org, Waiman Long Subject: [RFC PATCH 3/7] locking/rtqspinlock: Use static RT priority when in interrupt context Date: Tue, 3 Jan 2017 13:00:26 -0500 Message-Id: <1483466430-8028-4-git-send-email-longman@redhat.com> In-Reply-To: <1483466430-8028-1-git-send-email-longman@redhat.com> References: <1483466430-8028-1-git-send-email-longman@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Tue, 03 Jan 2017 18:01:17 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When in interrupt context, the priority of the interrupted task is meaningless. So static RT priority is assigned in this case to make sure that it can get lock ASAP to reduce latency to the interrupted task. Signed-off-by: Waiman Long --- kernel/locking/qspinlock_rt.h | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/kernel/locking/qspinlock_rt.h b/kernel/locking/qspinlock_rt.h index 69513d6..b6289fb 100644 --- a/kernel/locking/qspinlock_rt.h +++ b/kernel/locking/qspinlock_rt.h @@ -19,6 +19,13 @@ * * As RT qspinlock needs the whole pending byte, it cannot be used on kernel * configured to support 16K or more CPUs (CONFIG_NR_CPUS). + * + * In interrupt context, the priority of the interrupted task is not + * meaningful. So a fixed static RT priority is used and they won't go into + * the MCS wait queue. + * 1) Soft IRQ = 1 + * 2) Hard IRQ = MAX_RT_PRIO + * 3) NMI = MAX_RT_PRIO+1 */ #include @@ -60,11 +67,15 @@ static inline int rt_pending(int val) static bool rt_spin_trylock(struct qspinlock *lock) { struct __qspinlock *l = (void *)lock; - u8 prio = rt_task_priority(current); + struct task_struct *task = in_interrupt() ? NULL : current; + u8 prio; BUILD_BUG_ON(_Q_PENDING_BITS != 8); - if (!prio) + if (!task) + prio = in_nmi() ? MAX_RT_PRIO + 1 + : in_irq() ? MAX_RT_PRIO : 1; + else if (!(prio = rt_task_priority(task))) return false; /* -- 1.8.3.1