From: Ingo Molnar <mingo@elte.hu>
Date: Mon, 9 Jul 2007 16:51:58 +0000 (+0200)
Subject: sched: add rq_clock()/__rq_clock()
X-Git-Tag: v2.6.23-rc1~1262
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=20d315d42aed95423a7203e1d7e84086004b5a00;p=linux-2.6

sched: add rq_clock()/__rq_clock()

add rq_clock()/__rq_clock(), a robust wrapper around sched_clock(),
used by CFS. It protects against common type of sched_clock() problems
(caused by hardware): time warps forwards and backwards.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

diff --git a/kernel/sched.c b/kernel/sched.c
index 085418bedc..29eb227e33 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -388,6 +388,52 @@ static inline int cpu_of(struct rq *rq)
 #endif
 }
 
+/*
+ * Per-runqueue clock, as finegrained as the platform can give us:
+ */
+static unsigned long long __rq_clock(struct rq *rq)
+{
+	u64 prev_raw = rq->prev_clock_raw;
+	u64 now = sched_clock();
+	s64 delta = now - prev_raw;
+	u64 clock = rq->clock;
+
+	/*
+	 * Protect against sched_clock() occasionally going backwards:
+	 */
+	if (unlikely(delta < 0)) {
+		clock++;
+		rq->clock_warps++;
+	} else {
+		/*
+		 * Catch too large forward jumps too:
+		 */
+		if (unlikely(delta > 2*TICK_NSEC)) {
+			clock++;
+			rq->clock_overflows++;
+		} else {
+			if (unlikely(delta > rq->clock_max_delta))
+				rq->clock_max_delta = delta;
+			clock += delta;
+		}
+	}
+
+	rq->prev_clock_raw = now;
+	rq->clock = clock;
+
+	return clock;
+}
+
+static inline unsigned long long rq_clock(struct rq *rq)
+{
+	int this_cpu = smp_processor_id();
+
+	if (this_cpu == cpu_of(rq))
+		return __rq_clock(rq);
+
+	return rq->clock;
+}
+
 /*
  * The domain tree (rq->sd) is protected by RCU's quiescent state transition.
  * See detach_destroy_domains: synchronize_sched for details.