forked from mirrors/linux
c67ad917cb
per-cpu counters presently must iterate over all possible CPUs in the exhaustive percpu_counter_sum(). But it can be much better to only iterate over the presently-online CPUs. To do this, we must arrange for an offlined CPU's count to be spilled into the counter's central count. We can do this for all percpu_counters in the machine by linking them into a single global list and walking that list at CPU_DEAD time. (I hope. Might have race windows in which the percpu_counter_sum() count is inaccurate?) Cc: Gautham R Shenoy <ego@in.ibm.com> Cc: Oleg Nesterov <oleg@tv-sign.ru> Cc: 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>
108 lines
2.2 KiB
C
108 lines
2.2 KiB
C
#ifndef _LINUX_PERCPU_COUNTER_H
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#define _LINUX_PERCPU_COUNTER_H
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/*
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* A simple "approximate counter" for use in ext2 and ext3 superblocks.
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*
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* WARNING: these things are HUGE. 4 kbytes per counter on 32-way P4.
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*/
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#include <linux/spinlock.h>
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#include <linux/smp.h>
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#include <linux/list.h>
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#include <linux/threads.h>
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#include <linux/percpu.h>
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#include <linux/types.h>
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#ifdef CONFIG_SMP
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struct percpu_counter {
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spinlock_t lock;
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s64 count;
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#ifdef CONFIG_HOTPLUG_CPU
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struct list_head list; /* All percpu_counters are on a list */
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#endif
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s32 *counters;
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};
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#if NR_CPUS >= 16
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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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void percpu_counter_init(struct percpu_counter *fbc, s64 amount);
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void percpu_counter_destroy(struct percpu_counter *fbc);
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void percpu_counter_mod(struct percpu_counter *fbc, s32 amount);
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s64 percpu_counter_sum(struct percpu_counter *fbc);
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static inline s64 percpu_counter_read(struct percpu_counter *fbc)
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{
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return fbc->count;
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}
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/*
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* It is possible for the percpu_counter_read() to return a small negative
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* number for some counter which should never be negative.
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*
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*/
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static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
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{
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s64 ret = fbc->count;
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barrier(); /* Prevent reloads of fbc->count */
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if (ret >= 0)
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return ret;
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return 1;
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}
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#else
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struct percpu_counter {
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s64 count;
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};
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static inline void percpu_counter_init(struct percpu_counter *fbc, s64 amount)
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{
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fbc->count = amount;
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}
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static inline void percpu_counter_destroy(struct percpu_counter *fbc)
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{
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}
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static inline void
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percpu_counter_mod(struct percpu_counter *fbc, s32 amount)
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{
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preempt_disable();
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fbc->count += amount;
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preempt_enable();
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}
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static inline s64 percpu_counter_read(struct percpu_counter *fbc)
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{
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return fbc->count;
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}
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static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
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{
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return fbc->count;
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}
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static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
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{
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return percpu_counter_read_positive(fbc);
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}
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#endif /* CONFIG_SMP */
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static inline void percpu_counter_inc(struct percpu_counter *fbc)
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{
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percpu_counter_mod(fbc, 1);
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}
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static inline void percpu_counter_dec(struct percpu_counter *fbc)
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{
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percpu_counter_mod(fbc, -1);
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}
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#endif /* _LINUX_PERCPU_COUNTER_H */
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