netdev - Re: [PATCH 4/6] fs: Introduce a per_cpu nr

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Date:	Thu, 27 Nov 2008 10:32:57 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Ingo Molnar <mingo@...e.hu>, David Miller <davem@...emloft.net>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	kernel-testers@...r.kernel.org, Mike Galbraith <efault@....de>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>, travis <travis@....com>
Subject: Re: [PATCH 4/6] fs: Introduce a per_cpu nr_inodes

On Thu, 2008-11-27 at 00:32 +0100, Eric Dumazet wrote:
> Avoids cache line ping pongs between cpus and prepare next patch,
> because updates of nr_inodes metric dont need inode_lock anymore.
> 
> (socket8 bench result : 25s to 20.5s)
> 
> Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
> ---

> @@ -96,9 +96,40 @@ static DEFINE_MUTEX(iprune_mutex);
>   * Statistics gathering..
>   */
>  struct inodes_stat_t inodes_stat;
> +static DEFINE_PER_CPU(int, nr_inodes);
>  
>  static struct kmem_cache * inode_cachep __read_mostly;
>  
> +int get_nr_inodes(void)
> +{
> +	int cpu;
> +	int counter = 0;
> +
> +	for_each_possible_cpu(cpu)
> +	    counter += per_cpu(nr_inodes, cpu);
> +	if (counter < 0)
> +		counter = 0;
> +	return counter;
> +}

It would be good to get a cpu hotplug handler here and move to
for_each_online_cpu(). People are wanting distro's to be build with
NR_CPUS=4096.

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