sched/core: Rework rq->clock update skips
The original purpose of rq::skip_clock_update was to avoid 'costly' clock
updates for back to back wakeup-preempt pairs. The big problem with it
has always been that the rq variable is unaware of the context and
causes indiscrimiate clock skips.
Rework the entire thing and create a sense of context by only allowing
schedule() to skip clock updates. (XXX can we measure the cost of the
added store?)
By ensuring only schedule can ever skip an update, we guarantee we're
never more than 1 tick behind on the update.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: umgwanakikbuti@gmail.com
Link: http://lkml.kernel.org/r/20150105103554.432381549@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index bd23732..0870db2 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -558,8 +558,6 @@
#ifdef CONFIG_NO_HZ_FULL
unsigned long last_sched_tick;
#endif
- int skip_clock_update;
-
/* capture load from *all* tasks on this cpu: */
struct load_weight load;
unsigned long nr_load_updates;
@@ -588,6 +586,7 @@
unsigned long next_balance;
struct mm_struct *prev_mm;
+ unsigned int clock_skip_update;
u64 clock;
u64 clock_task;
@@ -704,6 +703,18 @@
return rq->clock_task;
}
+#define RQCF_REQ_SKIP 0x01
+#define RQCF_ACT_SKIP 0x02
+
+static inline void rq_clock_skip_update(struct rq *rq, bool skip)
+{
+ lockdep_assert_held(&rq->lock);
+ if (skip)
+ rq->clock_skip_update |= RQCF_REQ_SKIP;
+ else
+ rq->clock_skip_update &= ~RQCF_REQ_SKIP;
+}
+
#ifdef CONFIG_NUMA
enum numa_topology_type {
NUMA_DIRECT,