From: Waiman Long <waiman.long@hpe.com>
To: Tejun Heo <tj@kernel.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>,
Andreas Dilger <adilger.kernel@dilger.ca>,
Christoph Lameter <cl@linux.com>, <linux-ext4@vger.kernel.org>,
<linux-kernel@vger.kernel.org>,
Scott J Norton <scott.norton@hpe.com>,
Douglas Hatch <doug.hatch@hpe.com>,
Toshimitsu Kani <toshi.kani@hpe.com>
Subject: Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper functions
Date: Wed, 6 Apr 2016 15:52:39 -0400 [thread overview]
Message-ID: <57056907.20705@hpe.com> (raw)
In-Reply-To: <20160404160228.GW7822@mtj.duckdns.org>
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
next prev parent reply other threads:[~2016-04-06 20:08 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-02 3:09 [PATCH 0/3] ext4: Improve parallel I/O performance on NVDIMM Waiman Long
2016-04-02 3:09 ` [PATCH 1/3] ext4: Pass in DIO_SKIP_DIO_COUNT flag if inode_dio_begin() called Waiman Long
2016-04-02 3:09 ` [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper functions Waiman Long
2016-04-04 7:36 ` Nikolay Borisov
2016-04-04 17:11 ` Waiman Long
2016-04-04 19:09 ` Christoph Lameter
2016-04-06 21:53 ` Waiman Long
2016-04-04 16:02 ` Tejun Heo
2016-04-06 19:52 ` Waiman Long [this message]
2016-04-06 21:51 ` Waiman Long
2016-04-06 22:54 ` Tejun Heo
2016-04-07 15:58 ` Waiman Long
2016-04-07 16:06 ` Tejun Heo
2016-04-07 18:52 ` Waiman Long
2016-04-07 18:58 ` Tejun Heo
2016-04-07 20:37 ` Waiman Long
2016-04-07 20:41 ` Tejun Heo
2016-04-07 21:38 ` Waiman Long
2016-04-02 3:09 ` [PATCH 3/3] ext4: Make cache hits/misses per-cpu counts Waiman Long
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