Commit 179f7ebf authored by Eric Dumazet's avatar Eric Dumazet Committed by Linus Torvalds
Browse files

percpu_counter: FBC_BATCH should be a variable 



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, and get rid of NR_CPUS.

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.

We rename FBC_BATCH to percpu_counter_batch since its not a constant
anymore.

Signed-off-by: default avatarEric Dumazet <dada1@cosmosbay.com>
Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e3d5a27d

fs/ext4/ext4.h

+3 −3
Original line number Diff line number Diff line
@@ -1225,11 +1225,11 @@ do { \ 
} while (0)



#ifdef CONFIG_SMP

/* Each CPU can accumulate FBC_BATCH blocks in their local

/* Each CPU can accumulate percpu_counter_batch blocks in their local

 * counters. So we need to make sure we have free blocks more

 * than FBC_BATCH  * nr_cpu_ids. Also add a window of 4 times.

 * than percpu_counter_batch  * nr_cpu_ids. Also add a window of 4 times.

 */

#define EXT4_FREEBLOCKS_WATERMARK (4 * (FBC_BATCH * nr_cpu_ids))

#define EXT4_FREEBLOCKS_WATERMARK (4 * (percpu_counter_batch * nr_cpu_ids))

#else

#define EXT4_FREEBLOCKS_WATERMARK 0

#endif

fs/ext4/inode.c

+1 −1
Original line number Diff line number Diff line
@@ -2498,7 +2498,7 @@ static int ext4_nonda_switch(struct super_block *sb) 
	/*

	 * switch to non delalloc mode if we are running low

	 * on free block. The free block accounting via percpu

	 * counters can get slightly wrong with FBC_BATCH getting

	 * counters can get slightly wrong with percpu_counter_batch getting

	 * accumulated on each CPU without updating global counters

	 * Delalloc need an accurate free block accounting. So switch

	 * to non delalloc when we are near to error range.

include/linux/percpu_counter.h

+2 −6
Original line number Diff line number Diff line
@@ -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 percpu_counter_batch;



int percpu_counter_init(struct percpu_counter *fbc, s64 amount);

int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
@@ -39,7 +35,7 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc); 


static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)

{

	__percpu_counter_add(fbc, amount, FBC_BATCH);

	__percpu_counter_add(fbc, amount, percpu_counter_batch);

}



static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)

lib/percpu_counter.c

+14 −4
Original line number Diff line number Diff line
@@ -9,10 +9,8 @@ 
#include <linux/cpu.h>

#include <linux/module.h>



#ifdef CONFIG_HOTPLUG_CPU

static LIST_HEAD(percpu_counters);

static DEFINE_MUTEX(percpu_counters_lock);

#endif



void percpu_counter_set(struct percpu_counter *fbc, s64 amount)

{
@@ -111,13 +109,24 @@ void percpu_counter_destroy(struct percpu_counter *fbc) 
}

EXPORT_SYMBOL(percpu_counter_destroy);



#ifdef CONFIG_HOTPLUG_CPU

int percpu_counter_batch __read_mostly = 32;

EXPORT_SYMBOL(percpu_counter_batch);



static void compute_batch_value(void)

{

	int nr = num_online_cpus();



	percpu_counter_batch = max(32, nr*2);

}



static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,

					unsigned long action, void *hcpu)

{

#ifdef CONFIG_HOTPLUG_CPU

	unsigned int cpu;

	struct percpu_counter *fbc;



	compute_batch_value();

	if (action != CPU_DEAD)

		return NOTIFY_OK;
@@ -134,13 +143,14 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb, 
		spin_unlock_irqrestore(&fbc->lock, flags);

	}

	mutex_unlock(&percpu_counters_lock);

#endif

	return NOTIFY_OK;

}



static int __init percpu_counter_startup(void)

{

	compute_batch_value();

	hotcpu_notifier(percpu_counter_hotcpu_callback, 0);

	return 0;

}

module_init(percpu_counter_startup);
 
#endif

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