From 27c2f292d23983fac0e1f333a43424264c2e290b Mon Sep 17 00:00:00 2001
From: Simon Marlow <marlowsd@gmail.com>
Date: Wed, 11 Apr 2012 11:38:24 +0100
Subject: [PATCH] Improve the handling of threadDelay in the non-threaded RTS
Firstly, we were rounding up too much, such that the smallest delay
was 20ms. Secondly, there is no need to use millisecond resolution on
a 64-bit machine where we have room in the TSO to use the normal
nanosecond resolution that we use elsewhere in the RTS.
MERGED from commit 9d26519c20194abc3832578a55fbe31327519eeb
---
includes/rts/storage/TSO.h | 2 +-
rts/PrimOps.cmm | 6 +----
rts/posix/Select.c | 45 ++++++++++++++++++++++++++++----------
rts/posix/Select.h | 2 +-
4 files changed, 36 insertions(+), 19 deletions(-)
diff --git a/includes/rts/storage/TSO.h b/includes/rts/storage/TSO.h
index 5e54bff72c17..82f5a759481c 100644
--- a/includes/rts/storage/TSO.h
+++ b/includes/rts/storage/TSO.h
@@ -57,7 +57,7 @@ typedef union {
#if !defined(THREADED_RTS)
StgWord target;
// Only for the non-threaded RTS: the target time for a thread
- // blocked in threadDelay, in units of 10ms. This is a
+ // blocked in threadDelay, in units of 1ms. This is a
// compromise: we don't want to take up much space in the TSO. If
// you want better resolution for threadDelay, use -threaded.
#endif
diff --git a/rts/PrimOps.cmm b/rts/PrimOps.cmm
index 4cb3b8d85ccc..f07300fc8aa6 100644
--- a/rts/PrimOps.cmm
+++ b/rts/PrimOps.cmm
@@ -1838,11 +1838,7 @@ stg_delayzh
#else
- W_ time;
- (time) = foreign "C" getourtimeofday() [R1];
- // getourtimeofday() returns a value in units of 10ms
- // R1 is in microseconds, we need to (/ 10000), rounding up
- target = time + 1 + (R1 + 10000-1) / 10000;
+ (target) = foreign "C" getDelayTarget(R1) [R1];
StgTSO_block_info(CurrentTSO) = target;
diff --git a/rts/posix/Select.c b/rts/posix/Select.c
index 013b374d1add..a3f2ae301fcf 100644
--- a/rts/posix/Select.c
+++ b/rts/posix/Select.c
@@ -2,7 +2,10 @@
*
* (c) The GHC Team 1995-2002
*
- * Support for concurrent non-blocking I/O and thread waiting.
+ * Support for concurrent non-blocking I/O and thread waiting in the
+ * non-threaded RTS. In the threded RTS, this file is not used at
+ * all, instead we use the IO manager thread implemented in Haskell in
+ * the base package.
*
* ---------------------------------------------------------------------------*/
@@ -39,21 +42,39 @@
#if !defined(THREADED_RTS)
-/*
- * The threaded RTS uses an IO-manager thread in Haskell instead (see GHC.Conc)
- */
-
-#define LowResTimeToTime(t) (USToTime((t) * 10000))
+// The target time for a threadDelay is stored in a one-word quantity
+// in the TSO (tso->block_info.target). On a 32-bit machine we
+// therefore can't afford to use nanosecond resolution because it
+// would overflow too quickly, so instead we use millisecond
+// resolution.
+
+#if SIZEOF_VOID_P == 4
+#define LowResTimeToTime(t) (USToTime((t) * 1000))
+#define TimeToLowResTimeRoundDown(t) (TimeToUS(t) / 1000)
+#define TimeToLowResTimeRoundUp(t) ((TimeToUS(t) + 1000-1) / 1000)
+#else
+#define LowResTimeToTime(t) (t)
+#define TimeToLowResTimeRoundDown(t) (t)
+#define TimeToLowResTimeRoundUp(t) (t)
+#endif
/*
* Return the time since the program started, in LowResTime,
* rounded down.
- *
- * This is only used by posix/Select.c. It should probably go away.
*/
-LowResTime getourtimeofday(void)
+static LowResTime getLowResTimeOfDay(void)
+{
+ return TimeToLowResTimeRoundDown(stat_getElapsedTime());
+}
+
+/*
+ * For a given microsecond delay, return the target time in LowResTime.
+ */
+LowResTime getDelayTarget (HsInt us)
{
- return TimeToUS(stat_getElapsedTime()) / 10000;
+ // round up the target time, because we never want to sleep *less*
+ // than the desired amount.
+ return TimeToLowResTimeRoundUp(stat_getElapsedTime() + USToTime(us));
}
/* There's a clever trick here to avoid problems when the time wraps
@@ -136,7 +157,7 @@ awaitEvent(rtsBool wait)
*/
do {
- now = getourtimeofday();
+ now = getLowResTimeOfDay();
if (wakeUpSleepingThreads(now)) {
return;
}
@@ -246,7 +267,7 @@ awaitEvent(rtsBool wait)
/* check for threads that need waking up
*/
- wakeUpSleepingThreads(getourtimeofday());
+ wakeUpSleepingThreads(getLowResTimeOfDay());
/* If new runnable threads have arrived, stop waiting for
* I/O and run them.
diff --git a/rts/posix/Select.h b/rts/posix/Select.h
index 15fa00ac66b9..50d49d4ba5ab 100644
--- a/rts/posix/Select.h
+++ b/rts/posix/Select.h
@@ -12,6 +12,6 @@
// An absolute time value in units of 10ms.
typedef StgWord LowResTime;
-RTS_PRIVATE LowResTime getourtimeofday ( void );
+RTS_PRIVATE LowResTime getDelayTarget (HsInt us);
#endif /* POSIX_SELECT_H */
--
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