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

From: Daniel J Blueman
Date: Mon Dec 01 2014 - 14:16:15 EST

On 12/01/2014 01:49 PM, Bjorn Helgaas wrote:
On Tue, Nov 25, 2014 at 12:50 AM, Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx> 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

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.

For the Numachip case, it would be sufficient to add a call to set_vector_alloc_policy in the APIC driver, as this will always be preferred for local MSI handling.

I'll follow up with a patch in the next day or so; further support for other systems can be added later as and when tested.

Signed-off-by: Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx>
Cc: Daniel J Blueman <daniel@xxxxxxxxxxxxx>
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;
Daniel J Blueman
Principal Software Engineer, Numascale
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