On 04/04/2016 12:02 PM, Tejun Heo wrote:
Hello,
On Fri, Apr 01, 2016 at 11:09:37PM -0400, Waiman Long wrote:
...
+struct percpu_stats {
+ unsigned long __percpu *stats;
I'm not sure ulong is the best choice here. Atomic reads on 32bit are
nice but people often need 64bit counters for stats. It probably is a
better idea to use u64_stats_sync.
+/*
+ * Reset the all statistics counts to 0 in the percpu_stats structure
Proper function description please.
+ */
+static inline void percpu_stats_reset(struct percpu_stats *pcs)
Why is this function inline?
+{
+ 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;
+ }
I don't think this is acceptable.
+}
+
+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;
+}
Why inline the above functions?
+static inline void
+__percpu_stats_add(struct percpu_stats *pcs, int stat, int cnt)
+{
+ unsigned long *pstat;
+
+ if ((unsigned int)stat>= pcs->nstats)
+ return;
This is a critical bug. Please don't fail silently. BUG_ON(),
please.
Sure.
+ preempt_disable();
+ pstat = this_cpu_ptr(&pcs->stats[stat]);
+ *pstat += cnt;
+ preempt_enable();
+}
this_cpu_add() is atomic w.r.t. local operations.
Will use this_cpu_add().
+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;
Ditto.
+ for_each_possible_cpu(cpu)
+ sum += per_cpu(pcs->stats[stat], cpu);
+ return sum;
+}
Thanks.
Cheers,
Longman
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