bcache: A block layer cache
Does writethrough and writeback caching, handles unclean shutdown, and
has a bunch of other nifty features motivated by real world usage.
See the wiki at http://bcache.evilpiepirate.org for more.
Signed-off-by: Kent Overstreet <koverstreet@google.com>
diff --git a/drivers/md/bcache/stats.c b/drivers/md/bcache/stats.c
new file mode 100644
index 0000000..bf6cf95
--- /dev/null
+++ b/drivers/md/bcache/stats.c
@@ -0,0 +1,245 @@
+/*
+ * bcache stats code
+ *
+ * Copyright 2012 Google, Inc.
+ */
+
+#include "bcache.h"
+#include "stats.h"
+#include "btree.h"
+#include "request.h"
+#include "sysfs.h"
+
+/*
+ * We keep absolute totals of various statistics, and addionally a set of three
+ * rolling averages.
+ *
+ * Every so often, a timer goes off and rescales the rolling averages.
+ * accounting_rescale[] is how many times the timer has to go off before we
+ * rescale each set of numbers; that gets us half lives of 5 minutes, one hour,
+ * and one day.
+ *
+ * accounting_delay is how often the timer goes off - 22 times in 5 minutes,
+ * and accounting_weight is what we use to rescale:
+ *
+ * pow(31 / 32, 22) ~= 1/2
+ *
+ * So that we don't have to increment each set of numbers every time we (say)
+ * get a cache hit, we increment a single atomic_t in acc->collector, and when
+ * the rescale function runs it resets the atomic counter to 0 and adds its
+ * old value to each of the exported numbers.
+ *
+ * To reduce rounding error, the numbers in struct cache_stats are all
+ * stored left shifted by 16, and scaled back in the sysfs show() function.
+ */
+
+static const unsigned DAY_RESCALE = 288;
+static const unsigned HOUR_RESCALE = 12;
+static const unsigned FIVE_MINUTE_RESCALE = 1;
+static const unsigned accounting_delay = (HZ * 300) / 22;
+static const unsigned accounting_weight = 32;
+
+/* sysfs reading/writing */
+
+read_attribute(cache_hits);
+read_attribute(cache_misses);
+read_attribute(cache_bypass_hits);
+read_attribute(cache_bypass_misses);
+read_attribute(cache_hit_ratio);
+read_attribute(cache_readaheads);
+read_attribute(cache_miss_collisions);
+read_attribute(bypassed);
+
+SHOW(bch_stats)
+{
+ struct cache_stats *s =
+ container_of(kobj, struct cache_stats, kobj);
+#define var(stat) (s->stat >> 16)
+ var_print(cache_hits);
+ var_print(cache_misses);
+ var_print(cache_bypass_hits);
+ var_print(cache_bypass_misses);
+
+ sysfs_print(cache_hit_ratio,
+ DIV_SAFE(var(cache_hits) * 100,
+ var(cache_hits) + var(cache_misses)));
+
+ var_print(cache_readaheads);
+ var_print(cache_miss_collisions);
+ sysfs_hprint(bypassed, var(sectors_bypassed) << 9);
+#undef var
+ return 0;
+}
+
+STORE(bch_stats)
+{
+ return size;
+}
+
+static void bch_stats_release(struct kobject *k)
+{
+}
+
+static struct attribute *bch_stats_files[] = {
+ &sysfs_cache_hits,
+ &sysfs_cache_misses,
+ &sysfs_cache_bypass_hits,
+ &sysfs_cache_bypass_misses,
+ &sysfs_cache_hit_ratio,
+ &sysfs_cache_readaheads,
+ &sysfs_cache_miss_collisions,
+ &sysfs_bypassed,
+ NULL
+};
+static KTYPE(bch_stats);
+
+static void scale_accounting(unsigned long data);
+
+void bch_cache_accounting_init(struct cache_accounting *acc, struct closure *parent)
+{
+ kobject_init(&acc->total.kobj, &bch_stats_ktype);
+ kobject_init(&acc->five_minute.kobj, &bch_stats_ktype);
+ kobject_init(&acc->hour.kobj, &bch_stats_ktype);
+ kobject_init(&acc->day.kobj, &bch_stats_ktype);
+
+ closure_init(&acc->cl, parent);
+ init_timer(&acc->timer);
+ acc->timer.expires = jiffies + accounting_delay;
+ acc->timer.data = (unsigned long) acc;
+ acc->timer.function = scale_accounting;
+ add_timer(&acc->timer);
+}
+
+int bch_cache_accounting_add_kobjs(struct cache_accounting *acc,
+ struct kobject *parent)
+{
+ int ret = kobject_add(&acc->total.kobj, parent,
+ "stats_total");
+ ret = ret ?: kobject_add(&acc->five_minute.kobj, parent,
+ "stats_five_minute");
+ ret = ret ?: kobject_add(&acc->hour.kobj, parent,
+ "stats_hour");
+ ret = ret ?: kobject_add(&acc->day.kobj, parent,
+ "stats_day");
+ return ret;
+}
+
+void bch_cache_accounting_clear(struct cache_accounting *acc)
+{
+ memset(&acc->total.cache_hits,
+ 0,
+ sizeof(unsigned long) * 7);
+}
+
+void bch_cache_accounting_destroy(struct cache_accounting *acc)
+{
+ kobject_put(&acc->total.kobj);
+ kobject_put(&acc->five_minute.kobj);
+ kobject_put(&acc->hour.kobj);
+ kobject_put(&acc->day.kobj);
+
+ atomic_set(&acc->closing, 1);
+ if (del_timer_sync(&acc->timer))
+ closure_return(&acc->cl);
+}
+
+/* EWMA scaling */
+
+static void scale_stat(unsigned long *stat)
+{
+ *stat = ewma_add(*stat, 0, accounting_weight, 0);
+}
+
+static void scale_stats(struct cache_stats *stats, unsigned long rescale_at)
+{
+ if (++stats->rescale == rescale_at) {
+ stats->rescale = 0;
+ scale_stat(&stats->cache_hits);
+ scale_stat(&stats->cache_misses);
+ scale_stat(&stats->cache_bypass_hits);
+ scale_stat(&stats->cache_bypass_misses);
+ scale_stat(&stats->cache_readaheads);
+ scale_stat(&stats->cache_miss_collisions);
+ scale_stat(&stats->sectors_bypassed);
+ }
+}
+
+static void scale_accounting(unsigned long data)
+{
+ struct cache_accounting *acc = (struct cache_accounting *) data;
+
+#define move_stat(name) do { \
+ unsigned t = atomic_xchg(&acc->collector.name, 0); \
+ t <<= 16; \
+ acc->five_minute.name += t; \
+ acc->hour.name += t; \
+ acc->day.name += t; \
+ acc->total.name += t; \
+} while (0)
+
+ move_stat(cache_hits);
+ move_stat(cache_misses);
+ move_stat(cache_bypass_hits);
+ move_stat(cache_bypass_misses);
+ move_stat(cache_readaheads);
+ move_stat(cache_miss_collisions);
+ move_stat(sectors_bypassed);
+
+ scale_stats(&acc->total, 0);
+ scale_stats(&acc->day, DAY_RESCALE);
+ scale_stats(&acc->hour, HOUR_RESCALE);
+ scale_stats(&acc->five_minute, FIVE_MINUTE_RESCALE);
+
+ acc->timer.expires += accounting_delay;
+
+ if (!atomic_read(&acc->closing))
+ add_timer(&acc->timer);
+ else
+ closure_return(&acc->cl);
+}
+
+static void mark_cache_stats(struct cache_stat_collector *stats,
+ bool hit, bool bypass)
+{
+ if (!bypass)
+ if (hit)
+ atomic_inc(&stats->cache_hits);
+ else
+ atomic_inc(&stats->cache_misses);
+ else
+ if (hit)
+ atomic_inc(&stats->cache_bypass_hits);
+ else
+ atomic_inc(&stats->cache_bypass_misses);
+}
+
+void bch_mark_cache_accounting(struct search *s, bool hit, bool bypass)
+{
+ struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
+ mark_cache_stats(&dc->accounting.collector, hit, bypass);
+ mark_cache_stats(&s->op.c->accounting.collector, hit, bypass);
+#ifdef CONFIG_CGROUP_BCACHE
+ mark_cache_stats(&(bch_bio_to_cgroup(s->orig_bio)->stats), hit, bypass);
+#endif
+}
+
+void bch_mark_cache_readahead(struct search *s)
+{
+ struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
+ atomic_inc(&dc->accounting.collector.cache_readaheads);
+ atomic_inc(&s->op.c->accounting.collector.cache_readaheads);
+}
+
+void bch_mark_cache_miss_collision(struct search *s)
+{
+ struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
+ atomic_inc(&dc->accounting.collector.cache_miss_collisions);
+ atomic_inc(&s->op.c->accounting.collector.cache_miss_collisions);
+}
+
+void bch_mark_sectors_bypassed(struct search *s, int sectors)
+{
+ struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
+ atomic_add(sectors, &dc->accounting.collector.sectors_bypassed);
+ atomic_add(sectors, &s->op.c->accounting.collector.sectors_bypassed);
+}