linux-kernel - Re: [PATCH 4/4] kstat: modify kstat_irqs

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Date:	Sun, 11 Jan 2009 13:17:32 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Mike Travis <travis@....com>, Ingo Molnar <mingo@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] kstat: modify kstat_irqs_legacy to be variable
	sized


* Yinghai Lu <yinghai@...nel.org> wrote:

> On Sat, Jan 10, 2009 at 2:38 PM, Mike Travis <travis@....com> wrote:
> > Impact: reduce memory usage.
> >
> > Allocate kstat_irqs_legacy based on nr_cpu_ids to deal with this
> > memory usage bump when NR_CPUS bumped from 128 to 4096:
> >
> >     8192   +253952    262144 +3100%  kstat_irqs_legacy(.bss)
> >
> > This is only when CONFIG_SPARSE_IRQS=y.
> >
> > Signed-off-by: Mike Travis <travis@....com>
> > ---
> >  kernel/irq/handle.c |    9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > --- linux-2.6-for-ingo.orig/kernel/irq/handle.c
> > +++ linux-2.6-for-ingo/kernel/irq/handle.c
> > @@ -124,8 +124,7 @@ static struct irq_desc irq_desc_legacy[N
> >        }
> >  };
> >
> > -/* FIXME: use bootmem alloc ...*/
> > -static unsigned int kstat_irqs_legacy[NR_IRQS_LEGACY][NR_CPUS];
> > +static unsigned int *kstat_irqs_legacy;
> >
> >  int __init early_irq_init(void)
> >  {
> > @@ -146,9 +145,13 @@ int __init early_irq_init(void)
> >        /* allocate irq_desc_ptrs array based on nr_irqs */
> >        irq_desc_ptrs = alloc_bootmem(nr_irqs * sizeof(void *));
> >
> > +       /* allocate based on nr_cpu_ids */
> > +       kstat_irqs_legacy = alloc_bootmem(NR_IRQS_LEGACY * nr_cpu_ids *
> > +                                         sizeof(int));
> > +
> >        for (i = 0; i < legacy_count; i++) {
> >                desc[i].irq = i;
> > -               desc[i].kstat_irqs = kstat_irqs_legacy[i];
> > +               desc[i].kstat_irqs = kstat_irqs_legacy + i * NR_IRQS_LEGACY;
> 
> here should be
> 
> +               desc[i].kstat_irqs = kstat_irqs_legacy + i * nr_cpu_ids;

indeed - i fixed this in tip/cpus4096.

	Ingo
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