Re: Commit 34d76c41 causes linker errors on ia64 with NR_CPUS=4096

From: Jeff Mahoney
Date: Tue Oct 20 2009 - 10:49:33 EST


On 10/20/2009 10:18 AM, Jeff Mahoney wrote:
> On 10/20/2009 02:27 AM, Jiri Kosina wrote:
>> @@ -1627,11 +1623,10 @@ static int tg_shares_up(struct task_group *tg, void *data)
>> return 0;
>>
>> local_irq_save(flags);
>> - usd = &__get_cpu_var(update_shares_data);
>>
>> for_each_cpu(i, sched_domain_span(sd)) {
>> weight = tg->cfs_rq[i]->load.weight;
>> - usd->rq_weight[i] = weight;
>> + usd = *per_cpu_ptr(update_shares_data, i) = weight;
>>
>> /*
>> * If there are currently no tasks on the cpu pretend there
>
> I don't think this is what you want here.
>
> In the original version, usd is the percpu var using the current cpu. In
> your version, usd is the percpu var using i instead of the current cpu.
>
> I'll post my version of the patch shortly. I don't think keeping most of
> the original version is a bad thing. We can just allocate it dynamically
> instead.

This version fixes a build issue (__alignof__(unsigned long)) and fixes the
percpu lookup to be usd = percpu array pointer, usd[i] = actual variable.

-Jeff

From: Jiri Kosina <jkosina@xxxxxxx>
Subject: sched: move rq_weight data array out of .percpu

Commit 34d76c41 introduced percpu array update_shares_data, size of which
being proportional to NR_CPUS. Unfortunately this blows up ia64 for large
NR_CPUS configuration, as ia64 allows only 64k for .percpu section.

Fix this by allocating this array dynamically and keep only pointer to it
percpu.

Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
---
kernel/sched.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1564,11 +1564,7 @@ static unsigned long cpu_avg_load_per_ta

#ifdef CONFIG_FAIR_GROUP_SCHED

-struct update_shares_data {
- unsigned long rq_weight[NR_CPUS];
-};
-
-static DEFINE_PER_CPU(struct update_shares_data, update_shares_data);
+unsigned long *update_shares_data;

static void __set_se_shares(struct sched_entity *se, unsigned long shares);

@@ -1578,12 +1574,12 @@ static void __set_se_shares(struct sched
static void update_group_shares_cpu(struct task_group *tg, int cpu,
unsigned long sd_shares,
unsigned long sd_rq_weight,
- struct update_shares_data *usd)
+ unsigned long *usd)
{
unsigned long shares, rq_weight;
int boost = 0;

- rq_weight = usd->rq_weight[cpu];
+ rq_weight = usd[cpu];
if (!rq_weight) {
boost = 1;
rq_weight = NICE_0_LOAD;
@@ -1618,7 +1614,7 @@ static void update_group_shares_cpu(stru
static int tg_shares_up(struct task_group *tg, void *data)
{
unsigned long weight, rq_weight = 0, shares = 0;
- struct update_shares_data *usd;
+ unsigned long *usd;
struct sched_domain *sd = data;
unsigned long flags;
int i;
@@ -1627,11 +1623,11 @@ static int tg_shares_up(struct task_grou
return 0;

local_irq_save(flags);
- usd = &__get_cpu_var(update_shares_data);
+ usd = per_cpu_ptr(update_shares_data, smp_processor_id());

for_each_cpu(i, sched_domain_span(sd)) {
weight = tg->cfs_rq[i]->load.weight;
- usd->rq_weight[i] = weight;
+ usd[i] = weight;

/*
* If there are currently no tasks on the cpu pretend there
@@ -9407,6 +9403,10 @@ void __init sched_init(void)
#endif /* CONFIG_USER_SCHED */
#endif /* CONFIG_GROUP_SCHED */

+#ifdef CONFIG_FAIR_GROUP_SCHED
+ update_shares_data = __alloc_percpu(nr_cpu_ids * sizeof(unsigned long),
+ __alignof__(unsigned long));
+#endif
for_each_possible_cpu(i) {
struct rq *rq;



--
Jeff Mahoney
SUSE Labs
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