Use time based periods to age the writeback proportions,
which can adapt equally well to fast/slow devices. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iQIcBAABAgAGBQJQF0/wAAoJECvKgwp+S8JaszsP/16EO5F5mUCOFgncVRp+8R9U BxuKJ61j2R9ckHA+ngMEg72W5vJQds64cjywZnz6HMr0/+3tXUf4QBbU4/4sCeai 0lpK8MCKgp5KHHCxgO8zyoSaboankUgoDcbSmGJREV1WXoR8VWXsO9gXqiiH9XOe e8ADjds/YdxkQbOYDRgZKvLzwWS61K9Kwq5/56GASh2uflw7rkJZ38xqvGbo3YiQ IJJwOUYfJjFadIewYARQmkZZyWeAmtY0ADh15Z8pJt+iY4PgcDDlaWagwUH2Oaoi vhTFO4KnCjhSpc872et21g/jN/VrcQqzuUF/LUE9rW5irXeDZVCDrCQOuHQ+3Uo5 YuV3rpNABW/LU8AvtIwt9hUunaKUnrXaSluoL9LzH2VpH++JljQeR4yZ62Q5rpRs z4Bow25p7tlbcIJWzueMPdOFUr5s3P6XfQHoLVRWqN94eJ+Z1DPOgBlOain6cCUN oivPh4FxZfUscNmX8/7cHaTNEpGzJ0FzLPMNFnGQ2zwG0gk41fnMdWb19aVIE5GL /Q96TB24k/v+o1lbxGmyPi0L+Aq+NknvNm+p/YJHAAQrIpu5t2hPvka8/m7Nj7tu c3rM75RKiZkEI+3U6Ws1DhhQPtVcfNIVlNYQMGzlIndtK6T0ByueQ4eN5Z7ltjSE pS89rv2hyBw7yCaTU6ui =gZrM -----END PGP SIGNATURE----- Merge tag 'writeback-proportions' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux Pull writeback updates from Wu Fengguang: "Use time based periods to age the writeback proportions, which can adapt equally well to fast/slow devices." Fix up trivial conflict in comment in fs/sync.c * tag 'writeback-proportions' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux: writeback: Fix some comment errors block: Convert BDI proportion calculations to flexible proportions lib: Fix possible deadlock in flexible proportion code lib: Proportions with flexible period
This commit is contained in:
Linus Torvalds
commit
2e3ee61348
8 changed files with 448 additions and 50 deletions
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@ -11,7 +11,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
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rbtree.o radix-tree.o dump_stack.o timerqueue.o\
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idr.o int_sqrt.o extable.o prio_tree.o \
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sha1.o md5.o irq_regs.o reciprocal_div.o argv_split.o \
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proportions.o prio_heap.o ratelimit.o show_mem.o \
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proportions.o flex_proportions.o prio_heap.o ratelimit.o show_mem.o \
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is_single_threaded.o plist.o decompress.o
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lib-$(CONFIG_MMU) += ioremap.o
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272
lib/flex_proportions.c
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272
lib/flex_proportions.c
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@ -0,0 +1,272 @@
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/*
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* Floating proportions with flexible aging period
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*
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* Copyright (C) 2011, SUSE, Jan Kara <jack@suse.cz>
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*
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* The goal of this code is: Given different types of event, measure proportion
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* of each type of event over time. The proportions are measured with
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* exponentially decaying history to give smooth transitions. A formula
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* expressing proportion of event of type 'j' is:
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*
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* p_{j} = (\Sum_{i>=0} x_{i,j}/2^{i+1})/(\Sum_{i>=0} x_i/2^{i+1})
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*
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* Where x_{i,j} is j's number of events in i-th last time period and x_i is
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* total number of events in i-th last time period.
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*
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* Note that p_{j}'s are normalised, i.e.
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*
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* \Sum_{j} p_{j} = 1,
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*
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* This formula can be straightforwardly computed by maintaing denominator
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* (let's call it 'd') and for each event type its numerator (let's call it
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* 'n_j'). When an event of type 'j' happens, we simply need to do:
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* n_j++; d++;
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*
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* When a new period is declared, we could do:
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* d /= 2
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* for each j
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* n_j /= 2
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*
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* To avoid iteration over all event types, we instead shift numerator of event
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* j lazily when someone asks for a proportion of event j or when event j
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* occurs. This can bit trivially implemented by remembering last period in
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* which something happened with proportion of type j.
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*/
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#include <linux/flex_proportions.h>
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int fprop_global_init(struct fprop_global *p)
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{
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int err;
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p->period = 0;
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/* Use 1 to avoid dealing with periods with 0 events... */
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err = percpu_counter_init(&p->events, 1);
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if (err)
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return err;
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seqcount_init(&p->sequence);
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return 0;
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}
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void fprop_global_destroy(struct fprop_global *p)
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{
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percpu_counter_destroy(&p->events);
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}
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/*
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* Declare @periods new periods. It is upto the caller to make sure period
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* transitions cannot happen in parallel.
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*
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* The function returns true if the proportions are still defined and false
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* if aging zeroed out all events. This can be used to detect whether declaring
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* further periods has any effect.
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*/
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bool fprop_new_period(struct fprop_global *p, int periods)
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{
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u64 events;
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unsigned long flags;
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local_irq_save(flags);
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events = percpu_counter_sum(&p->events);
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/*
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* Don't do anything if there are no events.
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*/
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if (events <= 1) {
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local_irq_restore(flags);
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return false;
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}
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write_seqcount_begin(&p->sequence);
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if (periods < 64)
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events -= events >> periods;
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/* Use addition to avoid losing events happening between sum and set */
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percpu_counter_add(&p->events, -events);
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p->period += periods;
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write_seqcount_end(&p->sequence);
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local_irq_restore(flags);
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return true;
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}
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/*
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* ---- SINGLE ----
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*/
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int fprop_local_init_single(struct fprop_local_single *pl)
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{
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pl->events = 0;
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pl->period = 0;
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raw_spin_lock_init(&pl->lock);
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return 0;
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}
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void fprop_local_destroy_single(struct fprop_local_single *pl)
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{
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}
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static void fprop_reflect_period_single(struct fprop_global *p,
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struct fprop_local_single *pl)
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{
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unsigned int period = p->period;
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unsigned long flags;
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/* Fast path - period didn't change */
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if (pl->period == period)
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return;
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raw_spin_lock_irqsave(&pl->lock, flags);
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/* Someone updated pl->period while we were spinning? */
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if (pl->period >= period) {
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raw_spin_unlock_irqrestore(&pl->lock, flags);
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return;
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}
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/* Aging zeroed our fraction? */
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if (period - pl->period < BITS_PER_LONG)
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pl->events >>= period - pl->period;
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else
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pl->events = 0;
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pl->period = period;
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raw_spin_unlock_irqrestore(&pl->lock, flags);
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}
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/* Event of type pl happened */
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void __fprop_inc_single(struct fprop_global *p, struct fprop_local_single *pl)
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{
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fprop_reflect_period_single(p, pl);
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pl->events++;
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percpu_counter_add(&p->events, 1);
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}
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/* Return fraction of events of type pl */
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void fprop_fraction_single(struct fprop_global *p,
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struct fprop_local_single *pl,
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unsigned long *numerator, unsigned long *denominator)
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{
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unsigned int seq;
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s64 num, den;
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do {
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seq = read_seqcount_begin(&p->sequence);
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fprop_reflect_period_single(p, pl);
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num = pl->events;
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den = percpu_counter_read_positive(&p->events);
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} while (read_seqcount_retry(&p->sequence, seq));
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/*
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* Make fraction <= 1 and denominator > 0 even in presence of percpu
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* counter errors
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*/
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if (den <= num) {
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if (num)
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den = num;
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else
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den = 1;
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}
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*denominator = den;
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*numerator = num;
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}
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/*
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* ---- PERCPU ----
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*/
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#define PROP_BATCH (8*(1+ilog2(nr_cpu_ids)))
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int fprop_local_init_percpu(struct fprop_local_percpu *pl)
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{
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int err;
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err = percpu_counter_init(&pl->events, 0);
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if (err)
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return err;
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pl->period = 0;
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raw_spin_lock_init(&pl->lock);
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return 0;
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}
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void fprop_local_destroy_percpu(struct fprop_local_percpu *pl)
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{
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percpu_counter_destroy(&pl->events);
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}
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static void fprop_reflect_period_percpu(struct fprop_global *p,
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struct fprop_local_percpu *pl)
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{
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unsigned int period = p->period;
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unsigned long flags;
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/* Fast path - period didn't change */
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if (pl->period == period)
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return;
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raw_spin_lock_irqsave(&pl->lock, flags);
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/* Someone updated pl->period while we were spinning? */
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if (pl->period >= period) {
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raw_spin_unlock_irqrestore(&pl->lock, flags);
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return;
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}
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/* Aging zeroed our fraction? */
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if (period - pl->period < BITS_PER_LONG) {
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s64 val = percpu_counter_read(&pl->events);
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if (val < (nr_cpu_ids * PROP_BATCH))
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val = percpu_counter_sum(&pl->events);
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__percpu_counter_add(&pl->events,
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-val + (val >> (period-pl->period)), PROP_BATCH);
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} else
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percpu_counter_set(&pl->events, 0);
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pl->period = period;
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raw_spin_unlock_irqrestore(&pl->lock, flags);
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}
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/* Event of type pl happened */
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void __fprop_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl)
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{
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fprop_reflect_period_percpu(p, pl);
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__percpu_counter_add(&pl->events, 1, PROP_BATCH);
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percpu_counter_add(&p->events, 1);
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}
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void fprop_fraction_percpu(struct fprop_global *p,
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struct fprop_local_percpu *pl,
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unsigned long *numerator, unsigned long *denominator)
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{
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unsigned int seq;
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s64 num, den;
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do {
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seq = read_seqcount_begin(&p->sequence);
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fprop_reflect_period_percpu(p, pl);
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num = percpu_counter_read_positive(&pl->events);
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den = percpu_counter_read_positive(&p->events);
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} while (read_seqcount_retry(&p->sequence, seq));
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/*
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* Make fraction <= 1 and denominator > 0 even in presence of percpu
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* counter errors
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*/
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if (den <= num) {
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if (num)
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den = num;
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else
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den = 1;
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}
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*denominator = den;
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*numerator = num;
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}
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/*
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* Like __fprop_inc_percpu() except that event is counted only if the given
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* type has fraction smaller than @max_frac/FPROP_FRAC_BASE
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*/
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void __fprop_inc_percpu_max(struct fprop_global *p,
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struct fprop_local_percpu *pl, int max_frac)
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{
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if (unlikely(max_frac < FPROP_FRAC_BASE)) {
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unsigned long numerator, denominator;
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fprop_fraction_percpu(p, pl, &numerator, &denominator);
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if (numerator >
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(((u64)denominator) * max_frac) >> FPROP_FRAC_SHIFT)
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return;
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} else
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fprop_reflect_period_percpu(p, pl);
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__percpu_counter_add(&pl->events, 1, PROP_BATCH);
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percpu_counter_add(&p->events, 1);
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}
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