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: Eric Dumazet <dada1@cosmosbay.com> Acked-by: David S. Miller <davem@davemloft.net> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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4 changed files with 20 additions and 14 deletions
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@ -1225,11 +1225,11 @@ do { \
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} while (0)
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} while (0)
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#ifdef CONFIG_SMP
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#ifdef CONFIG_SMP
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/* Each CPU can accumulate FBC_BATCH blocks in their local
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/* Each CPU can accumulate percpu_counter_batch blocks in their local
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* counters. So we need to make sure we have free blocks more
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* counters. So we need to make sure we have free blocks more
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* than FBC_BATCH * nr_cpu_ids. Also add a window of 4 times.
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* than percpu_counter_batch * nr_cpu_ids. Also add a window of 4 times.
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*/
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*/
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#define EXT4_FREEBLOCKS_WATERMARK (4 * (FBC_BATCH * nr_cpu_ids))
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#define EXT4_FREEBLOCKS_WATERMARK (4 * (percpu_counter_batch * nr_cpu_ids))
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#else
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#else
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#define EXT4_FREEBLOCKS_WATERMARK 0
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#define EXT4_FREEBLOCKS_WATERMARK 0
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#endif
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#endif
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@ -2498,7 +2498,7 @@ static int ext4_nonda_switch(struct super_block *sb)
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/*
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/*
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* switch to non delalloc mode if we are running low
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* switch to non delalloc mode if we are running low
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* on free block. The free block accounting via percpu
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* on free block. The free block accounting via percpu
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* counters can get slightly wrong with FBC_BATCH getting
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* counters can get slightly wrong with percpu_counter_batch getting
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* accumulated on each CPU without updating global counters
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* accumulated on each CPU without updating global counters
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* Delalloc need an accurate free block accounting. So switch
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* Delalloc need an accurate free block accounting. So switch
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* to non delalloc when we are near to error range.
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* to non delalloc when we are near to error range.
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@ -24,11 +24,7 @@ struct percpu_counter {
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s32 *counters;
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s32 *counters;
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};
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};
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#if NR_CPUS >= 16
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extern int percpu_counter_batch;
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#define FBC_BATCH (NR_CPUS*2)
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#else
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#define FBC_BATCH (NR_CPUS*4)
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#endif
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int percpu_counter_init(struct percpu_counter *fbc, s64 amount);
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int percpu_counter_init(struct percpu_counter *fbc, s64 amount);
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int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
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int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
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@ -39,7 +35,7 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc);
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static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
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static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
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{
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{
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__percpu_counter_add(fbc, amount, FBC_BATCH);
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__percpu_counter_add(fbc, amount, percpu_counter_batch);
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}
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}
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static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
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static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
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@ -9,10 +9,8 @@
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#include <linux/cpu.h>
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#include <linux/cpu.h>
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#include <linux/module.h>
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#include <linux/module.h>
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#ifdef CONFIG_HOTPLUG_CPU
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static LIST_HEAD(percpu_counters);
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static LIST_HEAD(percpu_counters);
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static DEFINE_MUTEX(percpu_counters_lock);
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static DEFINE_MUTEX(percpu_counters_lock);
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#endif
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void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
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void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
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{
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{
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@ -111,13 +109,24 @@ void percpu_counter_destroy(struct percpu_counter *fbc)
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}
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}
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EXPORT_SYMBOL(percpu_counter_destroy);
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EXPORT_SYMBOL(percpu_counter_destroy);
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#ifdef CONFIG_HOTPLUG_CPU
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int percpu_counter_batch __read_mostly = 32;
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EXPORT_SYMBOL(percpu_counter_batch);
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static void compute_batch_value(void)
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{
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int nr = num_online_cpus();
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percpu_counter_batch = max(32, nr*2);
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}
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static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
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static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
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unsigned long action, void *hcpu)
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unsigned long action, void *hcpu)
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{
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{
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#ifdef CONFIG_HOTPLUG_CPU
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unsigned int cpu;
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unsigned int cpu;
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struct percpu_counter *fbc;
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struct percpu_counter *fbc;
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compute_batch_value();
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if (action != CPU_DEAD)
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if (action != CPU_DEAD)
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return NOTIFY_OK;
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return NOTIFY_OK;
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@ -134,13 +143,14 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
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spin_unlock_irqrestore(&fbc->lock, flags);
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spin_unlock_irqrestore(&fbc->lock, flags);
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}
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}
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mutex_unlock(&percpu_counters_lock);
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mutex_unlock(&percpu_counters_lock);
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#endif
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return NOTIFY_OK;
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return NOTIFY_OK;
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}
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}
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static int __init percpu_counter_startup(void)
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static int __init percpu_counter_startup(void)
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{
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{
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compute_batch_value();
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hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
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hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
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return 0;
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return 0;
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}
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}
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module_init(percpu_counter_startup);
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module_init(percpu_counter_startup);
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#endif
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