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Date: Tue, 27 Oct 2009 16:30:33 +0100 (CET)
From: Jiri Kosina <jkosina@...e.cz>
To: Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
Tejun Heo <tj@...nel.org>, Jeff Mahoney <jeffm@...e.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Tony Luck <tony.luck@...el.com>,
Fenghua Yu <fenghua.yu@...el.com>, linux-ia64@...r.kernel.org
Subject: Re: [PATCH 2/2] sched: move rq_weight data array out of .percpu
The previous version of the patch will actually not compile for
configurations with CONFIG_SMP=n && CONFIG_FAR_GROUP_SCHED=y
Tejun, please use the version below instead, which has proper ifdef in
place around the percpu allocation. Thanks.
From: Jiri Kosina <jkosina@...e.cz>
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.
The per-cpu handling doesn't impose significant performance penalty on
potentially contented path in tg_shares_up().
...
ffffffff8104337c: 65 48 8b 14 25 20 cd mov %gs:0xcd20,%rdx
ffffffff81043383: 00 00
ffffffff81043385: 48 c7 c0 00 e1 00 00 mov $0xe100,%rax
ffffffff8104338c: 48 c7 45 a0 00 00 00 movq $0x0,-0x60(%rbp)
ffffffff81043393: 00
ffffffff81043394: 48 c7 45 a8 00 00 00 movq $0x0,-0x58(%rbp)
ffffffff8104339b: 00
ffffffff8104339c: 48 01 d0 add %rdx,%rax
ffffffff8104339f: 49 8d 94 24 08 01 00 lea 0x108(%r12),%rdx
ffffffff810433a6: 00
ffffffff810433a7: b9 ff ff ff ff mov $0xffffffff,%ecx
ffffffff810433ac: 48 89 45 b0 mov %rax,-0x50(%rbp)
ffffffff810433b0: bb 00 04 00 00 mov $0x400,%ebx
ffffffff810433b5: 48 89 55 c0 mov %rdx,-0x40(%rbp)
...
After:
...
ffffffff8104337c: 65 8b 04 25 28 cd 00 mov %gs:0xcd28,%eax
ffffffff81043383: 00
ffffffff81043384: 48 98 cltq
ffffffff81043386: 49 8d bc 24 08 01 00 lea 0x108(%r12),%rdi
ffffffff8104338d: 00
ffffffff8104338e: 48 8b 15 d3 7f 76 00 mov 0x767fd3(%rip),%rdx # ffffffff817ab368 <update_shares_data>
ffffffff81043395: 48 8b 34 c5 00 ee 6d mov -0x7e921200(,%rax,8),%rsi
ffffffff8104339c: 81
ffffffff8104339d: 48 c7 45 a0 00 00 00 movq $0x0,-0x60(%rbp)
ffffffff810433a4: 00
ffffffff810433a5: b9 ff ff ff ff mov $0xffffffff,%ecx
ffffffff810433aa: 48 89 7d c0 mov %rdi,-0x40(%rbp)
ffffffff810433ae: 48 c7 45 a8 00 00 00 movq $0x0,-0x58(%rbp)
ffffffff810433b5: 00
ffffffff810433b6: bb 00 04 00 00 mov $0x400,%ebx
ffffffff810433bb: 48 01 f2 add %rsi,%rdx
ffffffff810433be: 48 89 55 b0 mov %rdx,-0x50(%rbp)
...
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
---
kernel/sched.c | 22 +++++++++++-----------
1 files changed, 11 insertions(+), 11 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index e886895..7c7ccbb 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1564,11 +1564,7 @@ static unsigned long cpu_avg_load_per_task(int cpu)
#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);
+static __read_mostly 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_entity *se, unsigned long shares);
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_rq_weight)
{
unsigned long shares, rq_weight;
int boost = 0;
- rq_weight = usd->rq_weight[cpu];
+ rq_weight = usd_rq_weight[cpu];
if (!rq_weight) {
boost = 1;
rq_weight = NICE_0_LOAD;
@@ -1618,7 +1614,7 @@ static void update_group_shares_cpu(struct task_group *tg, int cpu,
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_rq_weight;
struct sched_domain *sd = data;
unsigned long flags;
int i;
@@ -1627,11 +1623,11 @@ static int tg_shares_up(struct task_group *tg, void *data)
return 0;
local_irq_save(flags);
- usd = &__get_cpu_var(update_shares_data);
+ usd_rq_weight = 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_rq_weight[i] = weight;
/*
* If there are currently no tasks on the cpu pretend there
@@ -1652,7 +1648,7 @@ static int tg_shares_up(struct task_group *tg, void *data)
shares = tg->shares;
for_each_cpu(i, sched_domain_span(sd))
- update_group_shares_cpu(tg, i, shares, rq_weight, usd);
+ update_group_shares_cpu(tg, i, shares, rq_weight, usd_rq_weight);
local_irq_restore(flags);
@@ -9407,6 +9403,10 @@ void __init sched_init(void)
#endif /* CONFIG_USER_SCHED */
#endif /* CONFIG_GROUP_SCHED */
+#if defined CONFIG_FAIR_GROUP_SCHED && defined CONFIG_SMP
+ update_shares_data = __alloc_percpu(nr_cpu_ids * sizeof(unsigned long),
+ __alignof__(unsigned long));
+#endif
for_each_possible_cpu(i) {
struct rq *rq;
--
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