linux-kernel - Re: [RT LATENCY] 249 microsecond latency caused by slub's unfreeze

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Date:	Mon, 1 Apr 2013 17:46:03 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Clark Williams <clark@...hat.com>,
	Pekka Enberg <penberg@...nel.org>
Subject: Re: [RT LATENCY] 249 microsecond latency caused by slub's unfreeze_partials()
 code.

On 13-04-01 11:32 AM, Christoph Lameter wrote:

[...]

> @@ -4583,6 +4615,7 @@ static ssize_t min_partial_store(struct
>  }
>  SLAB_ATTR(min_partial);
> 
> +#ifdef CONFIG_CPU_PARTIAL

Above causes build failures when stats are on, because the
name is wrong and hence is never defined, and ....

>  static ssize_t cpu_partial_show(struct kmem_cache *s, char *buf)
>  {
>  	return sprintf(buf, "%u\n", s->cpu_partial);
> @@ -4605,6 +4638,7 @@ static ssize_t cpu_partial_store(struct
>  	return length;
>  }
>  SLAB_ATTR(cpu_partial);
> +#endif
> 
>  static ssize_t ctor_show(struct kmem_cache *s, char *buf)
>  {
> @@ -4644,6 +4678,7 @@ static ssize_t objects_partial_show(stru
>  }
>  SLAB_ATTR_RO(objects_partial);
> 
> +#ifdef CONFIG_SLUB_CPU_PARTIAL
>  static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
>  {
>  	int objects = 0;
> @@ -4674,6 +4709,7 @@ static ssize_t slabs_cpu_partial_show(st
>  	return len + sprintf(buf + len, "\n");
>  }
>  SLAB_ATTR_RO(slabs_cpu_partial);
> +#endif
> 
>  static ssize_t reclaim_account_show(struct kmem_cache *s, char *buf)
>  {
> @@ -4997,11 +5033,13 @@ STAT_ATTR(DEACTIVATE_BYPASS, deactivate_
>  STAT_ATTR(ORDER_FALLBACK, order_fallback);
>  STAT_ATTR(CMPXCHG_DOUBLE_CPU_FAIL, cmpxchg_double_cpu_fail);
>  STAT_ATTR(CMPXCHG_DOUBLE_FAIL, cmpxchg_double_fail);
> +#ifdef CONFIG_CPU_PARTIAL

...the same here, and ...

>  STAT_ATTR(CPU_PARTIAL_ALLOC, cpu_partial_alloc);
>  STAT_ATTR(CPU_PARTIAL_FREE, cpu_partial_free);
>  STAT_ATTR(CPU_PARTIAL_NODE, cpu_partial_node);
>  STAT_ATTR(CPU_PARTIAL_DRAIN, cpu_partial_drain);
>  #endif
> +#endif
> 
>  static struct attribute *slab_attrs[] = {
>  	&slab_size_attr.attr,
> @@ -5009,7 +5047,9 @@ static struct attribute *slab_attrs[] =
>  	&objs_per_slab_attr.attr,
>  	&order_attr.attr,
>  	&min_partial_attr.attr,
> +#ifdef CONFIG_CPU_PARTIAL

...here too.  All should be CONFIG_SLUB_CPU_PARTIAL

Thanks,
Paul.
--

>  	&cpu_partial_attr.attr,
> +#endif
>  	&objects_attr.attr,
>  	&objects_partial_attr.attr,
>  	&partial_attr.attr,
> @@ -5022,7 +5062,9 @@ static struct attribute *slab_attrs[] =
>  	&destroy_by_rcu_attr.attr,
>  	&shrink_attr.attr,
>  	&reserved_attr.attr,
> +#ifdef CONFIG_SLUB_CPU_PARTIAL
>  	&slabs_cpu_partial_attr.attr,
> +#endif
>  #ifdef CONFIG_SLUB_DEBUG
>  	&total_objects_attr.attr,
>  	&slabs_attr.attr,
> @@ -5064,11 +5106,13 @@ static struct attribute *slab_attrs[] =
>  	&order_fallback_attr.attr,
>  	&cmpxchg_double_fail_attr.attr,
>  	&cmpxchg_double_cpu_fail_attr.attr,
> +#ifdef CONFIG_SLUB_CPU_PARTIAL
>  	&cpu_partial_alloc_attr.attr,
>  	&cpu_partial_free_attr.attr,
>  	&cpu_partial_node_attr.attr,
>  	&cpu_partial_drain_attr.attr,
>  #endif
> +#endif
>  #ifdef CONFIG_FAILSLAB
>  	&failslab_attr.attr,
>  #endif
> Index: linux/init/Kconfig
> ===================================================================
> --- linux.orig/init/Kconfig	2013-04-01 10:27:05.908964674 -0500
> +++ linux/init/Kconfig	2013-04-01 10:31:46.497863625 -0500
> @@ -1514,6 +1514,17 @@ config SLOB
> 
>  endchoice
> 
> +config SLUB_CPU_PARTIAL
> +	default y
> +	depends on SLUB
> +	bool "SLUB per cpu partial cache"
> +	help
> +	  Per cpu partial caches accellerate objects allocation and freeing
> +	  that is local to a processor at the price of more indeterminism
> +	  in the latency of the free. On overflow these caches will be cleared
> +	  which requires the taking of locks that may cause latency spikes.
> +	  Typically one would choose no for a realtime system.
> +
>  config MMAP_ALLOW_UNINITIALIZED
>  	bool "Allow mmapped anonymous memory to be uninitialized"
>  	depends on EXPERT && !MMU
> 
--
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