linux-kernel - Re: [PATCH] irq: optimize init_kstat_irqs/init_copy_kstat

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Message-Id: <20090207002610.73ff7e6d.akpm@linux-foundation.org>
Date:	Sat, 7 Feb 2009 00:26:10 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] irq: optimize init_kstat_irqs/init_copy_kstat_irqs

On Fri, 06 Feb 2009 23:49:41 -0800 Yinghai Lu <yinghai@...nel.org> wrote:

> 
> Impact: even later type of kstat_irqs is changed
> 
> simplify and make init_kstat_irqs etc more type prof according to Andrew
> 
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> 
> ---
>  kernel/irq/handle.c       |   20 +++++++++++---------
>  kernel/irq/numa_migrate.c |   11 +++--------
>  2 files changed, 14 insertions(+), 17 deletions(-)
> 
> Index: linux-2.6/kernel/irq/handle.c
> ===================================================================
> --- linux-2.6.orig/kernel/irq/handle.c
> +++ linux-2.6/kernel/irq/handle.c
> @@ -82,19 +82,21 @@ static struct irq_desc irq_desc_init = {
>  
>  void init_kstat_irqs(struct irq_desc *desc, int cpu, int nr)
>  {
> -	unsigned long bytes;
> -	char *ptr;
>  	int node;
> -
> -	/* Compute how many bytes we need per irq and allocate them */
> -	bytes = nr * sizeof(unsigned int);
> +	void *ptr;
>  
>  	node = cpu_to_node(cpu);
> -	ptr = kzalloc_node(bytes, GFP_ATOMIC, node);
> -	printk(KERN_DEBUG "  alloc kstat_irqs on cpu %d node %d\n", cpu, node);
> +	ptr = kzalloc_node(nr * sizeof(*desc->kstat_irqs), GFP_ATOMIC, node);
>  
> -	if (ptr)
> -		desc->kstat_irqs = (unsigned int *)ptr;
> +	/*
> +	 * don't overwite if can not get new one
> +	 * init_copy_kstat_irqs() could still use old one
> +	 */
> +	if (ptr) {
> +		printk(KERN_DEBUG "  alloc kstat_irqs on cpu %d node %d\n",
> +			 cpu, node);
> +		desc->kstat_irqs = ptr;
> +	}

	else
		init_one_irq_desc() goes BUG.

>  }

Sorry, but it's just not acceptable for irq_to_desc_alloc_cpu() and
init_one_irq_desc() to go BUG if a GFP_ATOMIC allocation attempt
failed.

If this code is only called on kernel boot then OK, that's acceptable. 
But if that is the case then all this code should be marked
__init/__initdata.  And ack_apic_edge() sure doesn't look like a
boot-time-only function.

This is basic stuff which even a cursory review should have picked up.

Also, please go through all this code and convert WARN_ON(1) into
WARN(), and convert BUG_ON(1) into BUG().


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