linux-kernel - Re: [Patch Part3 v4 38/38] x86, irq: Add kernel parameter vector_alloc to set CPU vector allocation policy

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Date:	Mon, 1 Dec 2014 11:49:11 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Randy Dunlap <rdunlap@...radead.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Jonathan Corbet <corbet@....net>,
	"x86@...nel.org" <x86@...nel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...el.com>,
	Joerg Roedel <joro@...tes.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Daniel J Blueman <daniel@...ascale.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [Patch Part3 v4 38/38] x86, irq: Add kernel parameter
 vector_alloc to set CPU vector allocation policy

On Tue, Nov 25, 2014 at 12:50 AM, Jiang Liu <jiang.liu@...ux.intel.com> wrote:
> Parameter vector_alloc should be set to an integer with:
> bit 0:  enable allocating CPU vector from CPUs on device local node.
>         That's to allocate from cpumask_of_node(irq_data->node).
> bit 1: enable the default policy, which is to allocate from
>        apic->target_cpus().
>
> When allocating vectors, it tries all enabled policies from lower bit
> position to higher bit position.
>
> This option could be use to optimize interrupt distribution on large
> system such as NumaChip etc.

Why can't we figure this out automatically?  Having a kernel parameter
is a pain in the neck for users.

> Signed-off-by: Jiang Liu <jiang.liu@...ux.intel.com>
> Cc: Daniel J Blueman <daniel@...ascale.com>
> ---
>  Documentation/kernel-parameters.txt |    6 ++++++
>  arch/x86/kernel/apic/vector.c       |   11 +++++++++++
>  2 files changed, 17 insertions(+)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 4c81a860cc2b..a175c5016954 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -3709,6 +3709,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>         vector=         [IA-64,SMP]
>                         vector=percpu: enable percpu vector domain
>
> +       vector_alloc=   [x86,SMP]
> +                       vector_alloc=policy: policy is a bitmap, bit 0
> +                       for allocating CPU vector from CPUs on device local
> +                       node; bit 1 for the default policy to allocating from
> +                       apic->target_cpus(). All higher bits are reserved.
> +
>         video=          [FB] Frame buffer configuration
>                         See Documentation/fb/modedb.txt.
>
> diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c
> index 16de8906ee1e..1158843551c7 100644
> --- a/arch/x86/kernel/apic/vector.c
> +++ b/arch/x86/kernel/apic/vector.c
> @@ -79,6 +79,17 @@ void set_vector_alloc_policy(unsigned int policy)
>                 x86_vector_alloc_policy = policy | X86_VECTOR_POL_CALLER;
>  }
>
> +static int __init apic_parse_vector_policy(char *str)
> +{
> +       int policy;
> +
> +       if (get_option(&str, &policy) == 1)
> +               set_vector_alloc_policy(policy);
> +
> +       return 1;
> +}
> +__setup("vector_alloc=", apic_parse_vector_policy);
> +
>  static struct apic_chip_data *alloc_apic_chip_data(int node)
>  {
>         struct apic_chip_data *data;
> --
> 1.7.10.4
>
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