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Message-Id: <200903192310.52314.rusty@rustcorp.com.au>
Date: Thu, 19 Mar 2009 23:10:51 +1030
From: Rusty Russell <rusty@...tcorp.com.au>
To: Ingo Molnar <mingo@...e.hu>
Cc: Steven Rostedt <rostedt@...dmis.org>,
LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] cpumask: remove cpumask allocation from idle_balance
On Thursday 19 March 2009 15:22:20 Rusty Russell wrote:
> #ifdef CONFIG_USER_SCHED
> alloc_size *= 2;
> #endif
> +#ifdef CONFIG_CPUMASK_OFFSTACK
> + alloc_size *= num_possible_cpus() * cpumask_size();
> +#endif
Of course, this should be +=. Thanks for crash report, Ingo.
This time for sure,
Rusty.
===
Subject: [PATCH] cpumask: remove cpumask allocation from idle_balance
Impact: fix circular locking
Steven reports a circular locking from alloc_cpumask_var doing a wakeup.
We get rid of this using the tried-and-true technique of using a per-cpu
cpumask_var_t rather than doing an alloc every time. Ugly, but simple.
LKML-Reference: <alpine.DEB.2.00.0903181729360.31583@...dalf.stny.rr.com>
Reported-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
diff --git a/kernel/sched.c b/kernel/sched.c
index 5dabd80..48862d4 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3448,19 +3448,23 @@ find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
*/
#define MAX_PINNED_INTERVAL 512
+/* Working cpumask for load_balance and load_balance_newidle. */
+static DEFINE_PER_CPU(cpumask_var_t, load_balance_tmpmask);
+
/*
* Check this_cpu to ensure it is balanced within domain. Attempt to move
* tasks if there is an imbalance.
*/
static int load_balance(int this_cpu, struct rq *this_rq,
struct sched_domain *sd, enum cpu_idle_type idle,
- int *balance, struct cpumask *cpus)
+ int *balance)
{
int ld_moved, all_pinned = 0, active_balance = 0, sd_idle = 0;
struct sched_group *group;
unsigned long imbalance;
struct rq *busiest;
unsigned long flags;
+ struct cpumask *cpus = __get_cpu_var(load_balance_tmpmask);
cpumask_setall(cpus);
@@ -3615,8 +3619,7 @@ out:
* this_rq is locked.
*/
static int
-load_balance_newidle(int this_cpu, struct rq *this_rq, struct sched_domain *sd,
- struct cpumask *cpus)
+load_balance_newidle(int this_cpu, struct rq *this_rq, struct sched_domain *sd)
{
struct sched_group *group;
struct rq *busiest = NULL;
@@ -3624,6 +3627,7 @@ load_balance_newidle(int this_cpu, struct rq *this_rq, struct sched_domain *sd,
int ld_moved = 0;
int sd_idle = 0;
int all_pinned = 0;
+ struct cpumask *cpus = __get_cpu_var(load_balance_tmpmask);
cpumask_setall(cpus);
@@ -3764,10 +3768,6 @@ static void idle_balance(int this_cpu, struct rq *this_rq)
struct sched_domain *sd;
int pulled_task = 0;
unsigned long next_balance = jiffies + HZ;
- cpumask_var_t tmpmask;
-
- if (!alloc_cpumask_var(&tmpmask, GFP_ATOMIC))
- return;
for_each_domain(this_cpu, sd) {
unsigned long interval;
@@ -3778,7 +3778,7 @@ static void idle_balance(int this_cpu, struct rq *this_rq)
if (sd->flags & SD_BALANCE_NEWIDLE)
/* If we've pulled tasks over stop searching: */
pulled_task = load_balance_newidle(this_cpu, this_rq,
- sd, tmpmask);
+ sd);
interval = msecs_to_jiffies(sd->balance_interval);
if (time_after(next_balance, sd->last_balance + interval))
@@ -3793,7 +3793,6 @@ static void idle_balance(int this_cpu, struct rq *this_rq)
*/
this_rq->next_balance = next_balance;
}
- free_cpumask_var(tmpmask);
}
/*
@@ -3943,11 +3942,6 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
unsigned long next_balance = jiffies + 60*HZ;
int update_next_balance = 0;
int need_serialize;
- cpumask_var_t tmp;
-
- /* Fails alloc? Rebalancing probably not a priority right now. */
- if (!alloc_cpumask_var(&tmp, GFP_ATOMIC))
- return;
for_each_domain(cpu, sd) {
if (!(sd->flags & SD_LOAD_BALANCE))
@@ -3972,7 +3966,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
}
if (time_after_eq(jiffies, sd->last_balance + interval)) {
- if (load_balance(cpu, rq, sd, idle, &balance, tmp)) {
+ if (load_balance(cpu, rq, sd, idle, &balance)) {
/*
* We've pulled tasks over so either we're no
* longer idle, or one of our SMT siblings is
@@ -4006,8 +4000,6 @@ out:
*/
if (likely(update_next_balance))
rq->next_balance = next_balance;
-
- free_cpumask_var(tmp);
}
/*
@@ -8304,6 +8296,9 @@ void __init sched_init(void)
#ifdef CONFIG_USER_SCHED
alloc_size *= 2;
#endif
+#ifdef CONFIG_CPUMASK_OFFSTACK
+ alloc_size += num_possible_cpus() * cpumask_size();
+#endif
/*
* As sched_init() is called before page_alloc is setup,
* we use alloc_bootmem().
@@ -8341,6 +8336,12 @@ void __init sched_init(void)
ptr += nr_cpu_ids * sizeof(void **);
#endif /* CONFIG_USER_SCHED */
#endif /* CONFIG_RT_GROUP_SCHED */
+#ifdef CONFIG_CPUMASK_OFFSTACK
+ for_each_possible_cpu(i) {
+ per_cpu(load_balance_tmpmask, i) = (void *)ptr;
+ ptr += cpumask_size();
+ }
+#endif /* CONFIG_CPUMASK_OFFSTACK */
}
#ifdef CONFIG_SMP
--
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