linux-kernel - Re: [Xen-devel] [PATCH 2/9] xen/smp: Introduce a common structure to contain the IRQ name and interrupt line.

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Date:	Thu, 06 Jun 2013 08:16:39 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Cc:	"xen-devel" <xen-devel@...ts.xen.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 2/9] xen/smp: Introduce a common
 structure to contain the IRQ name and interrupt line.

>>> On 05.06.13 at 17:54, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:
> This patch adds a new structure to contain the common two things
> that each of the per-cpu interrupts need:
>  - an interrupt number,
>  - and the name of the interrupt (to be added in 'xen/smp: Don't leak
>    interrupt name when offlining').
> 
> This allows us to carry the tuple of the per-cpu interrupt data structure
> and expand it as we need in the future.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  arch/x86/xen/smp.c | 44 ++++++++++++++++++++++++--------------------
>  1 file changed, 24 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> index 19fc9f3..f5b29ec 100644
> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -39,11 +39,15 @@
>  
>  cpumask_var_t xen_cpu_initialized_map;
>  
> -static DEFINE_PER_CPU(int, xen_resched_irq);
> -static DEFINE_PER_CPU(int, xen_callfunc_irq);
> -static DEFINE_PER_CPU(int, xen_callfuncsingle_irq);
> -static DEFINE_PER_CPU(int, xen_irq_work);
> -static DEFINE_PER_CPU(int, xen_debug_irq) = -1;
> +struct xen_common_irq {
> +	int irq;
> +	char *name;
> +};
> +static DEFINE_PER_CPU(struct xen_common_irq, xen_resched_irq);
> +static DEFINE_PER_CPU(struct xen_common_irq, xen_callfunc_irq);
> +static DEFINE_PER_CPU(struct xen_common_irq, xen_callfuncsingle_irq);
> +static DEFINE_PER_CPU(struct xen_common_irq, xen_irq_work);
> +static DEFINE_PER_CPU(struct xen_common_irq, xen_debug_irq) = { .irq = -1 };

I have to admit that I'm quite puzzled by this still being massaged
the way it is, rather than getting converted to proper per-CPU
IRQs (i.e. with one global IRQ and only per-CPU event channels).
Not only conserves this on resources (irrespective of IRQs not
being a scarce resources anymore with SPARSE_IRQS), it also
makes /proc/interrupts output a lot more manageable on domains
with many vCPU-s.

I did this years ago for our kernels, but due to time constraints
can't offer to do the same for the upstream kernel until we get
ready to switch to using it in favor of the forward port.

Jan

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