Re: [PATCH] PER_CPU [4/4] - PER_CPU-irq_stat

[Anton Blanchard <anton@samba.org>]

 
Hi,

> Please find below one out of collection of patched that move NR_CPU array 
> variables to the per-cpu area.  Please consider applying, any comment will
> highly appreciated.

...

> diff -Nru a/kernel/softirq.c b/kernel/softirq.c
> --- a/kernel/softirq.c	2004-07-09 01:34:13 -07:00
> +++ b/kernel/softirq.c	2004-07-09 01:34:13 -07:00
> @@ -36,8 +36,8 @@
>   */
>  
>  #ifndef __ARCH_IRQ_STAT
> -irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;
> -EXPORT_SYMBOL(irq_stat);
> +DEFINE_PER_CPU(irq_cpustat_t, irq_stat) ____cacheline_maxaligned_in_smp;
> +EXPORT_PER_CPU_SYMBOL(irq_stat);
>  #endif

Is there a need for the cacheline alignment? We want to keep that per
cpu data area as packed as possible, we only want to explicitly pad if
we need to (eg other cpus are accessing that variable a lot).

Also it looks like we will have to push the above change into the other
architectures.

Anton