linux-kernel - Re: [PATCH v7 08/16] block,elevator: use new hashtable implementation

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Message-ID: <20121029122052.GB11733@Krystal>
Date:	Mon, 29 Oct 2012 08:20:52 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	torvalds@...ux-foundation.org, tj@...nel.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, paul.gortmaker@...driver.com,
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Subject: Re: [PATCH v7 08/16] block,elevator: use new hashtable
	implementation

* Sasha Levin (levinsasha928@...il.com) wrote:
[...]
> @@ -96,6 +97,8 @@ struct elevator_type
>  	struct list_head list;
>  };
>  
> +#define ELV_HASH_BITS 6
> +
>  /*
>   * each queue has an elevator_queue associated with it
>   */
> @@ -105,7 +108,7 @@ struct elevator_queue
>  	void *elevator_data;
>  	struct kobject kobj;
>  	struct mutex sysfs_lock;
> -	struct hlist_head *hash;
> +	DECLARE_HASHTABLE(hash, ELV_HASH_BITS);
>  	unsigned int registered:1;

Hrm, so this is moving "registered" out of the elevator_queue first
cache-line by turning the pointer into a 256 or 512 bytes hash table.

Maybe we should consider moving "registered" before the "hash" field ?

Thanks,

Mathieu

>  };
>  
> -- 
> 1.7.12.4
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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