From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756678AbdGXVpg (ORCPT ); Mon, 24 Jul 2017 17:45:36 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:57205 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755692AbdGXVou (ORCPT ); Mon, 24 Jul 2017 17:44:50 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, "Luis R. Rodriguez" , "Paul E. McKenney" Subject: [PATCH tip/core/rcu 08/15] swait: add idle variants which don't contribute to load average Date: Mon, 24 Jul 2017 14:44:37 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20170724214425.GA9665@linux.vnet.ibm.com> References: <20170724214425.GA9665@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17072421-0024-0000-0000-000002B5052D X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007419; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00892372; UDB=6.00446021; IPR=6.00672536; BA=6.00005489; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00016356; XFM=3.00000015; UTC=2017-07-24 21:44:48 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17072421-0025-0000-0000-000044DD5A44 Message-Id: <1500932684-10469-8-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-07-24_13:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1706020000 definitions=main-1707240332 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Luis R. Rodriguez" There are cases where folks are using an interruptible swait when using kthreads. This is rather confusing given you'd expect interruptible waits to be -- interruptible, but kthreads are not interruptible ! The reason for such practice though is to avoid having these kthreads contribute to the system load average. When systems are idle some kthreads may spend a lot of time blocking if using swait_event_timeout(). This would contribute to the system load average. On systems without preemption this would mean the load average of an idle system is bumped to 2 instead of 0. On systems with PREEMPT=y this would mean the load average of an idle system is bumped to 3 instead of 0. This adds proper API using TASK_IDLE to make such goals explicit and avoid confusion. Suggested-by: "Eric W. Biederman" Acked-by: "Eric W. Biederman" Tested-by: Paul E. McKenney Signed-off-by: Luis R. Rodriguez Signed-off-by: Paul E. McKenney --- include/linux/swait.h | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) diff --git a/include/linux/swait.h b/include/linux/swait.h index c1f9c62a8a50..4a4e180d0a35 100644 --- a/include/linux/swait.h +++ b/include/linux/swait.h @@ -169,4 +169,59 @@ do { \ __ret; \ }) +#define __swait_event_idle(wq, condition) \ + (void)___swait_event(wq, condition, TASK_IDLE, 0, schedule()) + +/** + * swait_event_idle - wait without system load contribution + * @wq: the waitqueue to wait on + * @condition: a C expression for the event to wait for + * + * The process is put to sleep (TASK_IDLE) until the @condition evaluates to + * true. The @condition is checked each time the waitqueue @wq is woken up. + * + * This function is mostly used when a kthread or workqueue waits for some + * condition and doesn't want to contribute to system load. Signals are + * ignored. + */ +#define swait_event_idle(wq, condition) \ +do { \ + if (condition) \ + break; \ + __swait_event_idle(wq, condition); \ +} while (0) + +#define __swait_event_idle_timeout(wq, condition, timeout) \ + ___swait_event(wq, ___wait_cond_timeout(condition), \ + TASK_IDLE, timeout, \ + __ret = schedule_timeout(__ret)) + +/** + * swait_event_idle_timeout - wait up to timeout without load contribution + * @wq: the waitqueue to wait on + * @condition: a C expression for the event to wait for + * @timeout: timeout at which we'll give up in jiffies + * + * The process is put to sleep (TASK_IDLE) until the @condition evaluates to + * true. The @condition is checked each time the waitqueue @wq is woken up. + * + * This function is mostly used when a kthread or workqueue waits for some + * condition and doesn't want to contribute to system load. Signals are + * ignored. + * + * Returns: + * 0 if the @condition evaluated to %false after the @timeout elapsed, + * 1 if the @condition evaluated to %true after the @timeout elapsed, + * or the remaining jiffies (at least 1) if the @condition evaluated + * to %true before the @timeout elapsed. + */ +#define swait_event_idle_timeout(wq, condition, timeout) \ +({ \ + long __ret = timeout; \ + if (!___wait_cond_timeout(condition)) \ + __ret = __swait_event_idle_timeout(wq, \ + condition, timeout); \ + __ret; \ +}) + #endif /* _LINUX_SWAIT_H */ -- 2.5.2