This patch introduces a set of simple per-cpu statictics count helper
functions that can be used by other kernel subsystems for keeping
track of the number of events that happens. It is per-cpu based to
reduce overhead and improve accuracy of the counter. Using per-cpu
counter is usually overkill for such purpose.
The following APIs are provided:
- int percpu_stats_init(struct percpu_stats *pcs, int num)
Initialize the per-cpu statictics counts structure which should have
the given number of statistics counts. Return -ENOMEM on error.
- void percpu_stats_destroy(struct percpu_stats *pcs)
Free the percpu memory allocated.
- void percpu_stats_inc(struct percpu_stats *pcs, int stat)
void percpu_stats_dec(struct percpu_stats *pcs, int stat)
Increment and decrement the given per-cpu statistics count.
- unsigned long percpu_stats_sum(struct percpu_stats *pcs, int stat)
Return the current aggregated sum of the given statistics count.
- void percpu_stats_reset(struct percpu_stats *pcs)
Clear all the statistics counts defined in the given percpu_stats
structure.
Signed-off-by: Waiman Long <Waiman.Long@xxxxxxx>
---
include/linux/percpu_stats.h | 103 ++++++++++++++++++++++++++++++++++++++++++
1 files changed, 103 insertions(+), 0 deletions(-)
create mode 100644 include/linux/percpu_stats.h
diff --git a/include/linux/percpu_stats.h b/include/linux/percpu_stats.h
new file mode 100644
index 0000000..a4f715e
--- /dev/null
+++ b/include/linux/percpu_stats.h
@@ -0,0 +1,103 @@
+#ifndef _LINUX_PERCPU_STATS_H
+#define _LINUX_PERCPU_STATS_H
+/*
+ * Simple per-cpu statistics counts that have less overhead than the
+ * per-cpu counters.
+ */
+#include <linux/percpu.h>
+#include <linux/types.h>
+
+struct percpu_stats {
+ unsigned long __percpu *stats;
+ int nstats; /* Number of statistics counts in stats array */
+};
+
+/*
+ * Reset the all statistics counts to 0 in the percpu_stats structure
+ */
+static inline void percpu_stats_reset(struct percpu_stats *pcs)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu) {
+ unsigned long *pstats = per_cpu_ptr(pcs->stats, cpu);
+ int stat;
+
+ for (stat = 0; stat < pcs->nstats; stat++, pstats++)
+ *pstats = 0;
+ }
+
+ /*
+ * If a statistics count is in the middle of being updated, it
+ * is possible that the above clearing may not work. So we need
+ * to double check again to make sure that the counters are really
+ * cleared. Still there is a still a very small chance that the
+ * second clearing does not work.
+ */
+ for_each_possible_cpu(cpu) {
+ unsigned long *pstats = per_cpu_ptr(pcs->stats, cpu);
+ int stat;
+
+ for (stat = 0; stat < pcs->nstats; stat++, pstats++)
+ if (*pstats)
+ *pstats = 0;
+ }
+}
+
+static inline int percpu_stats_init(struct percpu_stats *pcs, int num)
+{
+ pcs->nstats = num;
+ pcs->stats = __alloc_percpu(sizeof(unsigned long) * num,
+ __alignof__(unsigned long));
+ if (!pcs->stats)
+ return -ENOMEM;
+
+ percpu_stats_reset(pcs);
+ return 0;
+}
+
+static inline void percpu_stats_destroy(struct percpu_stats *pcs)
+{
+ free_percpu(pcs->stats);
+ pcs->stats = NULL;
+ pcs->nstats = 0;
+}
+
+static inline void
+__percpu_stats_add(struct percpu_stats *pcs, int stat, int cnt)
+{
+ unsigned long *pstat;
+
+ if ((unsigned int)stat >= pcs->nstats)
+ return;
+ preempt_disable();
+ pstat = this_cpu_ptr(&pcs->stats[stat]);
+ *pstat += cnt;
+ preempt_enable();
+}
+
+static inline void percpu_stats_inc(struct percpu_stats *pcs, int stat)
+{
+ __percpu_stats_add(pcs, stat, 1);
+}
+
+static inline void percpu_stats_dec(struct percpu_stats *pcs, int stat)
+{
+ __percpu_stats_add(pcs, stat, -1);
+}
+
+static inline unsigned long
+percpu_stats_sum(struct percpu_stats *pcs, int stat)
+{
+ int cpu;
+ unsigned long sum = 0;
+
+ if ((unsigned int)stat >= pcs->nstats)
+ return sum;
+
+ for_each_possible_cpu(cpu)
+ sum += per_cpu(pcs->stats[stat], cpu);
+ return sum;
+}
+
+#endif /* _LINUX_PERCPU_STATS_H */
--
1.7.1
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