linux-kernel - Re: [PATCH v5 tip/core/rcu 15/16] rcu: Make RCU-tasks wait for idle tasks

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Message-ID: <20140813172407.GM3588@twins.programming.kicks-ass.net>
Date:	Wed, 13 Aug 2014 19:24:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com,
	rafael@...nel.org
Subject: Re: [PATCH v5 tip/core/rcu 15/16] rcu: Make RCU-tasks wait for idle
 tasks

On Wed, Aug 13, 2014 at 04:42:19PM +0200, Peter Zijlstra wrote:
> Auditing all idle functions will be somewhat of a pain, but its entirely
> doable. Looking at this stuff, it appears we can clean it up massively;
> see how the generic cpuidle code already has the broadcast logic in, so
> we can remove that from the drivers by setting the right flags.
> 
> We can similarly pull out the leave_mm() call by adding a
> CPUIDLE_FLAG_TLB_FLUSH. At which point all we'd need to do is mark the
> intel_idle (and all other cpuidle_state::enter functions with __notrace.

This removes the broadcast stuff from intel_idle.c; processor_idle.c hurts
my brain, but something similar should be possible.

---
 drivers/idle/intel_idle.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 4d140bbbe100..6613d4ee60ce 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -508,11 +508,8 @@ static int intel_idle(struct cpuidle_device *dev,
 	unsigned long ecx = 1; /* break on interrupt flag */
 	struct cpuidle_state *state = &drv->states[index];
 	unsigned long eax = flg2MWAIT(state->flags);
-	unsigned int cstate;
 	int cpu = smp_processor_id();
 
-	cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK) + 1;
-
 	/*
 	 * leave_mm() to avoid costly and often unnecessary wakeups
 	 * for flushing the user TLB's associated with the active mm.
@@ -520,14 +517,8 @@ static int intel_idle(struct cpuidle_device *dev,
 	if (state->flags & CPUIDLE_FLAG_TLB_FLUSHED)
 		leave_mm(cpu);
 
-	if (!(lapic_timer_reliable_states & (1 << (cstate))))
-		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
-
 	mwait_idle_with_hints(eax, ecx);
 
-	if (!(lapic_timer_reliable_states & (1 << (cstate))))
-		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
-
 	return index;
 }
 
@@ -670,6 +661,7 @@ static int __init intel_idle_probe(void)
 {
 	unsigned int eax, ebx, ecx;
 	const struct x86_cpu_id *id;
+	int i;
 
 	if (max_cstate == 0) {
 		pr_debug(PREFIX "disabled\n");
@@ -705,6 +697,15 @@ static int __init intel_idle_probe(void)
 	else
 		on_each_cpu(__setup_broadcast_timer, (void *)true, 1);
 
+	for (i = 0; cpuidle_state_table[i].enter; i++) {
+		struct cpuidle_state *state = &cpuidle_state_table[i];
+		int cstate = ((flg2MWAIT(state->flags) >> MWAIT_SUBSTATE_SIZE) & 
+				MWAIT_CSTATE_MASK) + 1;
+
+		if (!(lapic_timer_reliable_states & (1 << cstate)))
+			state->flags |= CPUIDLE_FLAG_TIMER_STOP;
+	}
+
 	pr_debug(PREFIX "v" INTEL_IDLE_VERSION
 		" model 0x%X\n", boot_cpu_data.x86_model);
 

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