linux-kernel - Re: [PATCH 01/13] writeback: IO-less balance_dirty

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Date:	Thu, 18 Nov 2010 14:04:34 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
	Chris Mason <chris.mason@...cle.com>,
	Dave Chinner <david@...morbit.com>,
	Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
	Theodore Ts'o <tytso@....edu>, Mel Gorman <mel@....ul.ie>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm <linux-mm@...ck.org>, linux-fsdevel@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, tglx <tglx@...utronix.de>
Subject: Re: [PATCH 01/13] writeback: IO-less balance_dirty_pages()

On Wed, 2010-11-17 at 12:27 +0800, Wu Fengguang wrote:
> - avoid useless (eg. zero pause time) balance_dirty_pages() calls
> - avoid too small pause time (less than  10ms, which burns CPU power)
> - avoid too large pause time (more than 100ms, which hurts responsiveness)
> - avoid big fluctuations of pause times 

If you feel like playing with sub-jiffies timeouts (a way to avoid that
HZ=>100 assumption), the below (totally untested) patch might be of
help..


---
Subject: hrtimer: Provide io_schedule_timeout*() functions

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 include/linux/hrtimer.h |    7 +++++++
 kernel/hrtimer.c        |   15 +++++++++++++++
 kernel/sched.c          |   17 +++++++++++++++++
 3 files changed, 39 insertions(+), 0 deletions(-)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index dd9954b..9e0f67e 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -419,6 +419,13 @@ extern long hrtimer_nanosleep_restart(struct restart_block *restart_block);
 extern void hrtimer_init_sleeper(struct hrtimer_sleeper *sl,
 				 struct task_struct *tsk);
 
+extern int io_schedule_hrtimeout_range(ktime_t *expires, unsigned long delta,
+						const enum hrtimer_mode mode);
+extern int io_schedule_hrtimeout_range_clock(ktime_t *expires,
+		unsigned long delta, const enum hrtimer_mode mode, int clock);
+extern int io_schedule_hrtimeout(ktime_t *expires, const enum hrtimer_mode mode);
+
+
 extern int schedule_hrtimeout_range(ktime_t *expires, unsigned long delta,
 						const enum hrtimer_mode mode);
 extern int schedule_hrtimeout_range_clock(ktime_t *expires,
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 72206cf..ef2d93c 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -1838,6 +1838,14 @@ int __sched schedule_hrtimeout_range(ktime_t *expires, unsigned long delta,
 }
 EXPORT_SYMBOL_GPL(schedule_hrtimeout_range);
 
+int __sched io_schedule_hrtimeout_range(ktime_t *expires, unsigned long delta,
+				     const enum hrtimer_mode mode)
+{
+	return io_schedule_hrtimeout_range_clock(expires, delta, mode,
+					      CLOCK_MONOTONIC);
+}
+EXPORT_SYMBOL_GPL(io_schedule_hrtimeout_range);
+
 /**
  * schedule_hrtimeout - sleep until timeout
  * @expires:	timeout value (ktime_t)
@@ -1866,3 +1874,10 @@ int __sched schedule_hrtimeout(ktime_t *expires,
 	return schedule_hrtimeout_range(expires, 0, mode);
 }
 EXPORT_SYMBOL_GPL(schedule_hrtimeout);
+
+int __sched io_schedule_hrtimeout(ktime_t *expires,
+			       const enum hrtimer_mode mode)
+{
+	return io_schedule_hrtimeout_range(expires, 0, mode);
+}
+EXPORT_SYMBOL_GPL(io_schedule_hrtimeout);
diff --git a/kernel/sched.c b/kernel/sched.c
index d5564a8..ac84455 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5303,6 +5303,23 @@ long __sched io_schedule_timeout(long timeout)
 	return ret;
 }
 
+int __sched
+io_schedule_hrtimeout_range_clock(ktime_t *expires, unsigned long delta,
+			       const enum hrtimer_mode mode, int clock)
+{
+	struct rq *rq = raw_rq();
+	long ret;
+
+	delayacct_blkio_start();
+	atomic_inc(&rq->nr_iowait);
+	current->in_iowait = 1;
+	ret = schedule_hrtimeout_range_clock(expires, delta, mode, clock);
+	current->in_iowait = 0;
+	atomic_dec(&rq->nr_iowait);
+	delayacct_blkio_end();
+	return ret;
+}
+
 /**
  * sys_sched_get_priority_max - return maximum RT priority.
  * @policy: scheduling class.

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