linux-kernel - Re: [PATCH] sched: Introduce TASK_NOLOAD and TASK

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Date:	Mon, 11 May 2015 16:22:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Julian Anastasov <ja@....bg>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	neilb@...e.de
Subject: Re: [PATCH] sched: Introduce TASK_NOLOAD and TASK_IDLE

On Sat, May 09, 2015 at 11:49:01AM +0300, Julian Anastasov wrote:

> 	After checking our code in net/netfilter/ipvs/ip_vs_sync.c,
> sync_thread_master(), we may also need some wrappers:
> 
> - schedule_timeout_idle (instead of schedule_timeout call):
> 	__set_current_state(TASK_IDLE);
> 	return schedule_timeout(timeout);
> 
> 	- we here are really idle, so "N" looks ok

So I don't get the point of the schedule_timeout_*() stubs. What are
they for? Why would one use an unconditional schedule_timeout() call?
Isn't that what msleep() is for?

> - pair of __wait_event_idle(wq, condition) and
> 	wait_event_idle(wq, condition) macros
> 
> 	- we here are write-blocked for socket, not sure
> 	if this blocked vs idle difference is useful to
> 	represent, in new bit for this blocked state "B"=2048,
> 	with 2 TASK_NOLOAD variants: N(idle) and B(blocked,
> 	2|1024|2048, eg. for read-blocked or write-blocked).
> 	It will need additional argument 'state'/'blocked' for 
> 	*wait_event_idle().

Completely untested.

---
 include/linux/wait.h | 41 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 39 insertions(+), 2 deletions(-)

diff --git a/include/linux/wait.h b/include/linux/wait.h
index 2db83349865b..b9ef6bacf633 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -307,6 +307,26 @@ do {									\
 	__ret;								\
 })
 
+#define __wait_event_idle(wq, condition)				\
+	(void)___wait_event(wq, condition, TASK_IDLE, 0, 0,		\
+			    schedule())
+
+
+/**
+ * wait_event_idle - sleep until a condition get true; do not contribute to the loadavg
+ * @wq: the waitqueue to wait on
+ * @condition: a C expression for the event to wait for
+ *
+ * See wait_event()
+ */
+#define wait_event_idle(wq, condition)					\
+do {									\
+	might_sleep();							\
+	if (condition)							\
+		break;							\
+	__wait_event_idle(wq, condition);				\
+} while (0)
+
 #define __wait_event_timeout(wq, condition, timeout)			\
 	___wait_event(wq, ___wait_cond_timeout(condition),		\
 		      TASK_UNINTERRUPTIBLE, 0, timeout,			\
@@ -346,8 +366,8 @@ do {									\
 		      __ret = schedule_timeout(__ret); try_to_freeze())
 
 /*
- * like wait_event_timeout() -- except it uses TASK_INTERRUPTIBLE to avoid
- * increasing load and is freezable.
+ * like wait_event_timeout() -- except it uses TASK_INTERRUPTIBLE
+ * and is freezable.
  */
 #define wait_event_freezable_timeout(wq, condition, timeout)		\
 ({									\
@@ -358,6 +378,23 @@ do {									\
 	__ret;								\
 })
 
+#define __wait_event_idle_timeout(wq, condition, timeout)		\
+	___wait_event(wq, ___wait_cond_timeout(condition),		\
+		      TASK_IDLE, 0, timeout,				\
+		      __ret = schedule_timeout(__ret))
+
+/*
+ * like wait_event_timeout() -- except it uses TASK_IDLE to avoid loadavg
+ */
+#define wait_event_idle_timeout(wq, condition, timeout)			\
+({									\
+	long __ret = timeout;						\
+	might_sleep();							\
+	if (!___wait_cond_timeout(condition))				\
+		ret = __wait_event_idle_timeout(wq, condition, timeout);\
+	__ret;								\
+})
+
 #define __wait_event_cmd(wq, condition, cmd1, cmd2)			\
 	(void)___wait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0, 0,	\
 			    cmd1; schedule(); cmd2)
--
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