Date:	Wed, 01 May 2013 12:52:29 +0800
From:	Simon Jeons <simon.jeons@...il.com>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <ak@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH 1/2] Make the batch size of the percpu_counter configurable

Hi Tim,
On 04/30/2013 01:12 AM, Tim Chen wrote:
> Currently, there is a single, global, variable (percpu_counter_batch) that
> controls the batch sizes for every 'struct percpu_counter' on the system.
>
> However, there are some applications, e.g. memory accounting where it is
> more appropriate to scale the batch size according to the memory size.
> This patch adds the infrastructure to be able to change the batch sizes
> for each individual instance of 'struct percpu_counter'.
>
> I have chosen to implement the added field of batch as a pointer
> (by default point to percpu_counter_batch) instead
> of a static value.  The reason is the percpu_counter initialization
> can be called when we only have boot cpu and not all cpus are online.

What's the meaning of boot cpu? Do you mean cpu 0?

> and percpu_counter_batch value have yet to be udpated with a
> call to compute_batch_value function.
>
> Thanks to Dave Hansen and Andi Kleen for their comments and suggestions.
>
> Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
> ---
>   include/linux/percpu_counter.h | 20 +++++++++++++++++++-
>   lib/percpu_counter.c           | 23 ++++++++++++++++++++++-
>   2 files changed, 41 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
> index d5dd465..5ca7df5 100644
> --- a/include/linux/percpu_counter.h
> +++ b/include/linux/percpu_counter.h
> @@ -22,6 +22,7 @@ struct percpu_counter {
>   	struct list_head list;	/* All percpu_counters are on a list */
>   #endif
>   	s32 __percpu *counters;
> +	int *batch ____cacheline_aligned_in_smp;
>   };
>   
>   extern int percpu_counter_batch;
> @@ -40,11 +41,22 @@ void percpu_counter_destroy(struct percpu_counter *fbc);
>   void percpu_counter_set(struct percpu_counter *fbc, s64 amount);
>   void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch);
>   s64 __percpu_counter_sum(struct percpu_counter *fbc);
> +void __percpu_counter_batch_resize(struct percpu_counter *fbc, int *batch);
>   int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs);
>   
> +static inline int percpu_counter_and_batch_init(struct percpu_counter *fbc,
> +			s64 amount, int *batch)
> +{
> +	int ret = percpu_counter_init(fbc, amount);
> +
> +	if (batch && !ret)
> +		__percpu_counter_batch_resize(fbc, batch);
> +	return ret;
> +}
> +
>   static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
>   {
> -	__percpu_counter_add(fbc, amount, percpu_counter_batch);
> +	__percpu_counter_add(fbc, amount, *fbc->batch);
>   }
>   
>   static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
> @@ -95,6 +107,12 @@ static inline int percpu_counter_init(struct percpu_counter *fbc, s64 amount)
>   	return 0;
>   }
>   
> +static inline int percpu_counter_and_batch_init(struct percpu_counter *fbc,
> +			s64 amount, int *batch)
> +{
> +	return percpu_counter_init(fbc, amount);
> +}
> +
>   static inline void percpu_counter_destroy(struct percpu_counter *fbc)
>   {
>   }
> diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
> index ba6085d..a75951e 100644
> --- a/lib/percpu_counter.c
> +++ b/lib/percpu_counter.c
> @@ -116,6 +116,7 @@ int __percpu_counter_init(struct percpu_counter *fbc, s64 amount,
>   	lockdep_set_class(&fbc->lock, key);
>   	fbc->count = amount;
>   	fbc->counters = alloc_percpu(s32);
> +	fbc->batch = &percpu_counter_batch;
>   	if (!fbc->counters)
>   		return -ENOMEM;
>   
> @@ -131,6 +132,26 @@ int __percpu_counter_init(struct percpu_counter *fbc, s64 amount,
>   }
>   EXPORT_SYMBOL(__percpu_counter_init);
>   
> +void __percpu_counter_batch_resize(struct percpu_counter *fbc, int *batch)
> +{
> +	unsigned long flags;
> +	int cpu;
> +
> +	if (!batch)
> +		return;
> +
> +	raw_spin_lock_irqsave(&fbc->lock, flags);
> +	for_each_online_cpu(cpu) {
> +		s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
> +		fbc->count += *pcount;
> +		*pcount = 0;
> +	}
> +	*batch = max(*batch, percpu_counter_batch);
> +	fbc->batch = batch;
> +	raw_spin_unlock_irqrestore(&fbc->lock, flags);
> +}
> +EXPORT_SYMBOL(__percpu_counter_batch_resize);
> +
>   void percpu_counter_destroy(struct percpu_counter *fbc)
>   {
>   	if (!fbc->counters)
> @@ -196,7 +217,7 @@ int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
>   
>   	count = percpu_counter_read(fbc);
>   	/* Check to see if rough count will be sufficient for comparison */
> -	if (abs(count - rhs) > (percpu_counter_batch*num_online_cpus())) {
> +	if (abs(count - rhs) > ((*fbc->batch)*num_online_cpus())) {
>   		if (count > rhs)
>   			return 1;
>   		else

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