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.
> + preempt_disable();
> + pstat = this_cpu_ptr(&pcs->stats[stat]);
> + *pstat += cnt;
> + preempt_enable();
> +}
this_cpu_add() is atomic w.r.t. local operations.
> +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.
--
tejun
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