Messages in this thread | | | Date | Wed, 6 Apr 2016 17:51:45 -0400 | From | Waiman Long <> | Subject | Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper functions |
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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.
Got that, will incorporate 64-bit counter support for 32-bit architecture.
>> +/* >> + * Reset the all statistics counts to 0 in the percpu_stats structure > Proper function description please.
Sure. Will do that for all the functions.
>> + */ >> +static inline void percpu_stats_reset(struct percpu_stats *pcs) > Why is this function inline?
It doesn't need to be inlined, but I need to add a lib/percpu_stats.c file to hold the function which I will do in my v2 patch.
> >> +{ >> + 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.
I am not sure what you mean here by not acceptable. Please enlighten me on that.
>> +} >> + >> +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?
Will move this function to lib/percpu_stats.c.
>> +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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