In this second version I guarded hotcpu_notifier() call by
a #ifdef CONFIG_HOTPLUG_CPU
I wonder why hotcpu_notifier() is not a null op if !CONFIG_HOTPLUG_CPU
Thank you
[PATCH] percpu_counter: FBC_BATCH might be too big
For NR_CPUS >= 16 values, FBC_BATCH is 2*NR_CPUS
Considering more and more distros are using high NR_CPUS values,
it makes sense to use a more sensible value for FBC_BATCH.
A sensible value is 2*num_online_cpus(), with a minimum value of 32
(This minimum value helps branch prediction in __percpu_counter_add())
We already have a hotcpu notifier, so we can adjust FBC_BATCH dynamically.
Signed-off-by: Eric Dumazet <dada1@xxxxxxxxxxxxx>
Acked-by: David S. Miller <davem@xxxxxxxxxxxxx>
Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
include/linux/percpu_counter.h | 6 +-----
lib/percpu_counter.c | 16 +++++++++++++++-
2 files changed, 16 insertions(+), 6 deletions(-)
diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index 9007ccd..c42a184 100644
--- a/include/linux/percpu_counter.h
+++ b/include/linux/percpu_counter.h
@@ -24,11 +24,7 @@ struct percpu_counter {
s32 *counters;
};
-#if NR_CPUS >= 16
-#define FBC_BATCH (NR_CPUS*2)
-#else
-#define FBC_BATCH (NR_CPUS*4)
-#endif
+extern int FBC_BATCH;
int percpu_counter_init(struct percpu_counter *fbc, s64 amount);
int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index a866389..e21ce7c 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -114,6 +114,16 @@ void percpu_counter_destroy(struct percpu_counter *fbc)
}
EXPORT_SYMBOL(percpu_counter_destroy);
+int FBC_BATCH __read_mostly = 32;
+EXPORT_SYMBOL(FBC_BATCH);
+
+static void compute_batch_value(void)
+{
+ int nr = num_online_cpus();
+
+ FBC_BATCH = max(32, nr*2);
+}
+
#ifdef CONFIG_HOTPLUG_CPU
static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
unsigned long action, void *hcpu)
@@ -121,6 +131,7 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
unsigned int cpu;
struct percpu_counter *fbc;
+ compute_batch_value();
if (action != CPU_DEAD)
return NOTIFY_OK;
@@ -139,11 +150,14 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
mutex_unlock(&percpu_counters_lock);
return NOTIFY_OK;
}
+#endif
static int __init percpu_counter_startup(void)
{
+ compute_batch_value();
+#ifdef CONFIG_HOTPLUG_CPU
hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
+#endif
return 0;
}
module_init(percpu_counter_startup);
-#endif
--
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