On Mon, Aug 26, 2019 at 04:14:36PM +0200, Peter Zijlstra wrote:
> (XXX, we should probably move the schedule_timeout() thing into its own
> patch)
A better version here...
---
Subject: sched,time: Allow better constprop/DCE for schedule_timeout()
If timeout is constant and MAX_SCHEDULE_TIMEOUT, it would be nice to
allow to optimize away everything timeout.
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
include/linux/sched.h | 13 ++++++++++++-
kernel/time/timer.c | 52 ++++++++++++++++++++++++---------------------------
2 files changed, 36 insertions(+), 29 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f0edee94834a..6003e96bce52 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -214,7 +214,18 @@ extern void scheduler_tick(void);
#define MAX_SCHEDULE_TIMEOUT LONG_MAX
-extern long schedule_timeout(long timeout);
+extern long __schedule_timeout(long timeout);
+
+static inline long schedule_timeout(long timeout)
+{
+ if (__builtin_constant_p(timeout) && timeout == MAX_SCHEDULE_TIMEOUT) {
+ schedule();
+ return timeout;
+ }
+
+ return __schedule_timeout(timeout);
+}
+
extern long schedule_timeout_interruptible(long timeout);
extern long schedule_timeout_killable(long timeout);
extern long schedule_timeout_uninterruptible(long timeout);
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 0e315a2e77ae..912ae56b96b8 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1851,38 +1851,34 @@ static void process_timeout(struct timer_list *t)
* jiffies will be returned. 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 process_timer 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.
- */
+ /*
+ * We could take MAX_SCHEDULE_TIMEOUT from one of the negative values,
+ * but I'd like to return a valid offset (>= 0) to allow the caller to
+ * do everything it wants with the retval.
+ */
+ if (timeout == MAX_SCHEDULE_TIMEOUT) {
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 "
+ return 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;
@@ -1898,10 +1894,10 @@ signed long __sched schedule_timeout(signed long
timeout)
timeout = expire - jiffies;
- out:
+out:
return timeout < 0 ? 0 : timeout;
}
-EXPORT_SYMBOL(schedule_timeout);
+EXPORT_SYMBOL(__schedule_timeout);
/*
* We can use __set_current_state() here because schedule_timeout() calls
