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Date: Fri, 02 May 2008 21:56:26 +0200
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
To: Mike Galbraith <efault@....de>
Cc: Frans Pop <elendil@...net.nl>,
Parag Warudkar <parag.warudkar@...il.com>,
Ingo Molnar <mingo@...e.hu>,
LKML <linux-kernel@...r.kernel.org>,
Guillaume Chazarain <guichaz@...oo.fr>,
Andi Kleen <andi@...stfloor.org>
Subject: 'global' rq->clock (was Re: Horrendous Audio Stutter - current git)
On Fri, 2008-05-02 at 21:27 +0200, Mike Galbraith wrote:
That's a quite horrible patch for some of us, but I think I know why you
did that, and I think your fancy Q6600 has a stable enough TSC to pull
it off.
Let me try and come up with something slightly less horrible
> Fix undesirable rq.clock update noops.
>
> Signed-off-by: Mike Galbraith <efault@....de>
>
> Index: linux-2.6.26.git/kernel/sched.c
> ===================================================================
> --- linux-2.6.26.git.orig/kernel/sched.c
> +++ linux-2.6.26.git/kernel/sched.c
> @@ -668,9 +668,6 @@ static void __update_rq_clock(struct rq
> s64 delta = now - prev_raw;
> u64 clock = rq->clock;
>
> -#ifdef CONFIG_SCHED_DEBUG
> - WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());
> -#endif
> /*
> * Protect against sched_clock() occasionally going backwards:
> */
> @@ -3009,8 +3006,8 @@ static void double_rq_lock(struct rq *rq
> spin_lock(&rq1->lock);
> }
> }
> - update_rq_clock(rq1);
> - update_rq_clock(rq2);
> + __update_rq_clock(rq1);
> + __update_rq_clock(rq2);
> }
>
> /*
> @@ -3860,7 +3857,7 @@ redo:
> /* Attempt to move tasks */
> double_lock_balance(this_rq, busiest);
> /* this_rq->clock is already updated */
> - update_rq_clock(busiest);
> + __update_rq_clock(busiest);
> ld_moved = move_tasks(this_rq, this_cpu, busiest,
> imbalance, sd, CPU_NEWLY_IDLE,
> &all_pinned);
> @@ -3959,8 +3956,8 @@ static void active_load_balance(struct r
>
> /* move a task from busiest_rq to target_rq */
> double_lock_balance(busiest_rq, target_rq);
> - update_rq_clock(busiest_rq);
> - update_rq_clock(target_rq);
> + __update_rq_clock(busiest_rq);
> + __update_rq_clock(target_rq);
>
> /* Search for an sd spanning us and the target CPU. */
> for_each_domain(target_cpu, sd) {
> Index: linux-2.6.26.git/kernel/sched_fair.c
> ===================================================================
> --- linux-2.6.26.git.orig/kernel/sched_fair.c
> +++ linux-2.6.26.git/kernel/sched_fair.c
> @@ -1221,7 +1221,7 @@ static void check_preempt_wakeup(struct
> int se_depth, pse_depth;
>
> if (unlikely(rt_prio(p->prio))) {
> - update_rq_clock(rq);
> + __update_rq_clock(rq);
> update_curr(cfs_rq);
> resched_task(curr);
> return;
>
Ok, the the below would need something that relates tick_timestamp's to
one another.. probably sucks without it..
OTOH, Andi said he was working on a fastish global sched_clock() thingy,
Andi got a link to that code?
Index: linux-2.6-2/kernel/sched.c
===================================================================
--- linux-2.6-2.orig/kernel/sched.c
+++ linux-2.6-2/kernel/sched.c
@@ -560,6 +560,7 @@ struct rq {
unsigned long next_balance;
struct mm_struct *prev_mm;
+ spinlock_t clock_lock;
u64 clock, prev_clock_raw;
s64 clock_max_delta;
@@ -657,20 +658,25 @@ static inline void update_last_tick_seen
}
#endif
+#define cpu_rq(cpu) (&per_cpu(runqueues, (cpu)))
+#define this_rq() (&__get_cpu_var(runqueues))
+#define task_rq(p) cpu_rq(task_cpu(p))
+#define cpu_curr(cpu) (cpu_rq(cpu)->curr)
+
/*
* Update the per-runqueue clock, as finegrained as the platform can give
* us, but without assuming monotonicity, etc.:
*/
-static void __update_rq_clock(struct rq *rq)
+static void ___update_rq_clock(struct rq *rq, u64 now)
{
u64 prev_raw = rq->prev_clock_raw;
- u64 now = sched_clock();
s64 delta = now - prev_raw;
u64 clock = rq->clock;
#ifdef CONFIG_SCHED_DEBUG
WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());
#endif
+ spin_lock(&rq->clock_lock);
/*
* Protect against sched_clock() occasionally going backwards:
*/
@@ -699,12 +705,31 @@ static void __update_rq_clock(struct rq
rq->prev_clock_raw = now;
rq->clock = clock;
+ spin_unlock(&rq->clock_lock);
+}
+
+static void __update_rq_clock(struct rq *rq)
+{
+ ___update_rq_clock(rq, sched_clock());
+}
+
+static void __update_remote_rq_clock(struct rq *rq)
+{
+ u64 now = sched_clock();
+ struct rq *this_rq = this_rq();
+
+ now -= this_rq->tick_timestamp;
+ now += rq->tick_timestamp;
+
+ ___update_rq_clock(rq, now);
}
static void update_rq_clock(struct rq *rq)
{
if (likely(smp_processor_id() == cpu_of(rq)))
__update_rq_clock(rq);
+ else
+ __update_remote_rq_clock(rq);
}
/*
@@ -717,11 +742,6 @@ static void update_rq_clock(struct rq *r
#define for_each_domain(cpu, __sd) \
for (__sd = rcu_dereference(cpu_rq(cpu)->sd); __sd; __sd = __sd->parent)
-#define cpu_rq(cpu) (&per_cpu(runqueues, (cpu)))
-#define this_rq() (&__get_cpu_var(runqueues))
-#define task_rq(p) cpu_rq(task_cpu(p))
-#define cpu_curr(cpu) (cpu_rq(cpu)->curr)
-
/*
* Tunables that become constants when CONFIG_SCHED_DEBUG is off:
*/
@@ -8147,6 +8167,7 @@ void __init sched_init(void)
rq = cpu_rq(i);
spin_lock_init(&rq->lock);
+ spin_lock_init(&rq->clock_lock);
lockdep_set_class(&rq->lock, &rq->rq_lock_key);
rq->nr_running = 0;
rq->clock = 1;
--
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