linux-kernel - [PATCH v6 1/6] sched: Add function single_task_running to let a task check if it is the only task running on a cpu

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Message-ID: <1406827788.2970.948.camel@schen9-DESK>
Date:	Thu, 31 Jul 2014 10:29:48 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>,
	"H. Peter Anvin" <hpa@...or.com>,
	"David S.Miller" <davem@...emloft.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Cc:	Chandramouli Narayanan <mouli@...ux.intel.com>,
	Vinodh Gopal <vinodh.gopal@...el.com>,
	James Guilford <james.guilford@...el.com>,
	Wajdi Feghali <wajdi.k.feghali@...el.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Jussi Kivilinna <jussi.kivilinna@....fi>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tadeusz Struk <tadeusz.struk@...el.com>, tkhai@...dex.ru,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v6 1/6] sched: Add function single_task_running to let a
 task check if it is the only task running on a cpu

This function will help an async task processing batched jobs from
workqueue decide if it wants to keep processing on more chunks of batched
work that can be delayed, or to accumulate more work for more efficient
batched processing later.

If no other tasks are running on the cpu, the batching process can take
advantgae of the available cpu cycles to a make decision to continue
processing the existing accumulated work to minimize delay,
otherwise it will yield.

Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
---
 include/linux/sched.h |  1 +
 kernel/sched/core.c   | 12 ++++++++++++
 2 files changed, 13 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7cb07fd..eefa943 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -168,6 +168,7 @@ extern int nr_threads;
 DECLARE_PER_CPU(unsigned long, process_counts);
 extern int nr_processes(void);
 extern unsigned long nr_running(void);
+extern bool single_task_running(void);
 extern unsigned long nr_iowait(void);
 extern unsigned long nr_iowait_cpu(int cpu);
 extern unsigned long this_cpu_load(void);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9cae286..03c8675 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2283,6 +2283,18 @@ unsigned long nr_running(void)
 	return sum;
 }
 
+/*
+ * Check if only the current task is running on the cpu.
+ */
+bool single_task_running(void)
+{
+	if (cpu_rq(smp_processor_id())->nr_running == 1)
+		return true;
+	else
+		return false;
+}
+EXPORT_SYMBOL(single_task_running);
+
 unsigned long long nr_context_switches(void)
 {
 	int i;
-- 
1.7.11.7



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