linux-kernel - Re: [RFC] [Patch 4/4] lock contention tracking slimmed down

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Date:	Thu, 07 Jun 2007 10:17:01 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Martin Peschke <mp3@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, jbaron@...hat.com,
	rostedt@...dmis.org, billh@...ppy.monkey.org, mingo@...e.hu,
	linux-s390@...r.kernel.org
Subject: Re: [RFC] [Patch 4/4] lock contention tracking slimmed down

On Wed, 2007-06-06 at 23:34 +0200, Martin Peschke wrote:

> +#ifdef CONFIG_LOCK_STAT
> +enum lock_stat_enum {
> +	LOCK_STAT_CONT,
> +	LOCK_STAT_WAIT_READ,
> +	LOCK_STAT_WAIT_WRITE,
> +	LOCK_STAT_HOLD_READ,
> +	LOCK_STAT_HOLD_WRITE,
> +	_LOCK_STAT_NUMBER
> +};
> +#endif
> +
>  /*
>   * The lock-class itself:
>   */
> @@ -117,30 +129,11 @@ struct lock_class {
>  	int				name_version;
>  
>  #ifdef CONFIG_LOCK_STAT
> -	unsigned long			contention_point[4];
> +	struct statistic		stat[_LOCK_STAT_NUMBER];
> +	struct statistic_coll		stat_coll;
>  #endif
>  };


sizeof(struct statistic_coll) = 16+64+8+8+4+8+8 = 116
sizeof(struct statistic) = 4+4+8+8+8+8+8+4+8+4+4 = 68
                         + 8*NR_CPUS
			 + kmalloc_size(obj)*nr_cpu_ids


4 objs with size 40, gives 4*64 = 256 * nr_cpu_ids
1 obj with size 32 + more


for 2048 total classes this gives:

2048 * (116+68) = 376832

for each active class this adds per cpu:

  8+256+32+some = 296+

we have around 1400 locks in the kernel, this would give 414400 per cpu.

vs the old code:

2048*(4*8) = 65536
+
2048*(4*4*8 + 4*8) = 327680 per cpu

worst case

I'm not convinced 300 lines less code is worth that extra bloat.

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