From: Waiman Long <waiman.long@hpe.com>
Subject: Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper
 functions
Date: Mon, 4 Apr 2016 13:11:47 -0400
Message-ID: <5702A053.5030404@hpe.com>
References: <1459566578-30221-1-git-send-email-Waiman.Long@hpe.com> <1459566578-30221-3-git-send-email-Waiman.Long@hpe.com> <57021969.8050504@kyup.com>
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Cc: Theodore Ts'o <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Tejun Heo <tj@kernel.org>, 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>
To: Nikolay Borisov <kernel@kyup.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <57021969.8050504@kyup.com>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-ext4.vger.kernel.org

On 04/04/2016 03:36 AM, Nikolay Borisov wrote:
>
> On 04/02/2016 06:09 AM, Waiman Long wrote:
>> 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@hpe.com>
>> ---
>>   include/linux/percpu_stats.h |  103 ++++++++++++++++++++++++++++++++++++++++++
>>   1 files changed, 103 insertions(+), 0 deletions(-)
>>   create mode 100644 include/linux/percpu_stats.h
> Just one minor nit below.
> [..]
>> +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();
>> +}
> pstat = get_cpu_ptr(&pcs->stats[stat]);
> *pstat += cnt;
> put_cpu_ptr(&pcs->stats[stat]);
>
> It will generate identical code but this one uses APIs, making the
> intention clearer. But as I said this is just a minor nit.
>
> you can add my Reviewed-by: Nikolay Borisov<kernel@kyup.com>  for this
> particular patch.

Yes, that will certainly make it look nicer. I will update the patch 
once I get feedback from my other ext4 patches.

Cheers,
Longman