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Date: Wed, 21 Aug 2013 14:48:49 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Arjan van de Ven <arjan@...ux.intel.com>,
Fernando Luis Vázquez Cao
<fernando_b1@....ntt.co.jp>,
Frederic Weisbecker <fweisbec@...il.com>,
Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
LKML <linux-kernel@...r.kernel.org>,
Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock
On Wed, Aug 21, 2013 at 01:35:51PM +0200, Oleg Nesterov wrote:
> > > Btw. Whatever we do, can't we unify io_schedule/io_schedule_timeout?
> >
> > I suppose we could, a timeout of MAX_SCHEDULE_TIMEOUT will act like a
> > regular schedule, but it gets all the overhead of doing
> > schedule_timeout(). So I don't think its a win.
>
> Well, the only overhead is "if(to == MAX_SCHEDULE_TIMEOUT)" at the start.
> I don't think it makes sense to copy-and-paste the identical code to
> avoid it. But please ignore, this is really minor and off-topic.
Ah, so the 'problem' is that schedule_timeout() doesn't live in
kernel/sched/core.c and we thus get an extra function call (which are
somewhat expensive on some archs).
That said, I suppose we could do something like the below, that should
allow the compiler to DTRT.
---
include/linux/sched.h | 35 ++++++++++++++++++++++---
kernel/sched/core.c | 22 +++++-----------
kernel/timer.c | 67 ++++++++++--------------------------------------
3 files changed, 52 insertions(+), 72 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 50d04b9..112960c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -303,10 +303,37 @@ extern char __sched_text_start[], __sched_text_end[];
extern int in_sched_functions(unsigned long addr);
#define MAX_SCHEDULE_TIMEOUT LONG_MAX
-extern signed long schedule_timeout(signed long timeout);
-extern signed long schedule_timeout_interruptible(signed long timeout);
-extern signed long schedule_timeout_killable(signed long timeout);
-extern signed long schedule_timeout_uninterruptible(signed long timeout);
+extern long __schedule_timeout(long timeout);
+
+static inline long schedule_timeout(long timeout)
+{
+ if (timeout == MAX_SCHEDULE_TIMEOUT) {
+ schedule();
+ return timeout;
+ }
+ return __schedule_timeout(timeout);
+}
+
+/*
+ * We can use __set_current_state() here because schedule_timeout() calls
+ * schedule() unconditionally.
+ */
+static inline long schedule_timeout_interruptible(long timeout)
+{
+ __set_current_state(TASK_INTERRUPTIBLE);
+ return schedule_timeout(timeout);
+}
+static inline long schedule_timeout_killable(long timeout)
+{
+ __set_current_state(TASK_KILLABLE);
+ return schedule_timeout(timeout);
+}
+static inline long schedule_timeout_uninterruptible(long timeout)
+{
+ __set_current_state(TASK_UNINTERRUPTIBLE);
+ return schedule_timeout(timeout);
+}
+
asmlinkage void schedule(void);
extern void schedule_preempt_disabled(void);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f737871..ef2cddd 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3937,21 +3937,6 @@ EXPORT_SYMBOL_GPL(yield_to);
* This task is about to go to sleep on IO. Increment rq->nr_iowait so
* that process accounting knows that this is a task in IO wait state.
*/
-void __sched io_schedule(void)
-{
- struct rq *rq = raw_rq();
-
- delayacct_blkio_start();
- atomic_inc(&rq->nr_iowait);
- blk_flush_plug(current);
- current->in_iowait = 1;
- schedule();
- current->in_iowait = 0;
- atomic_dec(&rq->nr_iowait);
- delayacct_blkio_end();
-}
-EXPORT_SYMBOL(io_schedule);
-
long __sched io_schedule_timeout(long timeout)
{
struct rq *rq = raw_rq();
@@ -3968,6 +3953,13 @@ long __sched io_schedule_timeout(long timeout)
return ret;
}
+void __sched io_schedule(void)
+{
+ io_schedule_timeout(MAX_SCHEDULE_TIMEOUT);
+}
+EXPORT_SYMBOL(io_schedule);
+
+
/**
* sys_sched_get_priority_max - return maximum RT priority.
* @policy: scheduling class.
diff --git a/kernel/timer.c b/kernel/timer.c
index 15bc1b4..8244ce0 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1429,38 +1429,24 @@ static void process_timeout(unsigned long __data)
*
* In all cases the return value is guaranteed to be non-negative.
*/
-signed long __sched schedule_timeout(signed long timeout)
+signed long __sched __schedule_timeout(signed long timeout)
{
struct timer_list timer;
unsigned long expire;
- switch (timeout)
- {
- case MAX_SCHEDULE_TIMEOUT:
- /*
- * These two special cases are useful to be comfortable
- * in the caller. Nothing more. We could take
- * MAX_SCHEDULE_TIMEOUT from one of the negative value
- * but I' d like to return a valid offset (>=0) to allow
- * the caller to do everything it want with the retval.
- */
- schedule();
- goto out;
- default:
- /*
- * Another bit of PARANOID. Note that the retval will be
- * 0 since no piece of kernel is supposed to do a check
- * for a negative retval of schedule_timeout() (since it
- * should never happens anyway). You just have the printk()
- * that will tell you if something is gone wrong and where.
- */
- if (timeout < 0) {
- printk(KERN_ERR "schedule_timeout: wrong timeout "
+ /*
+ * Another bit of PARANOID. Note that the retval will be 0 since no
+ * piece of kernel is supposed to do a check for a negative retval of
+ * schedule_timeout() (since it should never happens anyway). You just
+ * have the printk() that will tell you if something is gone wrong and
+ * where.
+ */
+ if (timeout < 0) {
+ printk(KERN_ERR "schedule_timeout: wrong timeout "
"value %lx\n", timeout);
- dump_stack();
- current->state = TASK_RUNNING;
- goto out;
- }
+ dump_stack();
+ current->state = TASK_RUNNING;
+ goto out;
}
expire = timeout + jiffies;
@@ -1478,32 +1464,7 @@ signed long __sched schedule_timeout(signed long timeout)
out:
return timeout < 0 ? 0 : timeout;
}
-EXPORT_SYMBOL(schedule_timeout);
-
-/*
- * We can use __set_current_state() here because schedule_timeout() calls
- * schedule() unconditionally.
- */
-signed long __sched schedule_timeout_interruptible(signed long timeout)
-{
- __set_current_state(TASK_INTERRUPTIBLE);
- return schedule_timeout(timeout);
-}
-EXPORT_SYMBOL(schedule_timeout_interruptible);
-
-signed long __sched schedule_timeout_killable(signed long timeout)
-{
- __set_current_state(TASK_KILLABLE);
- return schedule_timeout(timeout);
-}
-EXPORT_SYMBOL(schedule_timeout_killable);
-
-signed long __sched schedule_timeout_uninterruptible(signed long timeout)
-{
- __set_current_state(TASK_UNINTERRUPTIBLE);
- return schedule_timeout(timeout);
-}
-EXPORT_SYMBOL(schedule_timeout_uninterruptible);
+EXPORT_SYMBOL(__schedule_timeout);
static int __cpuinit init_timers_cpu(int cpu)
{
--
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