linux-kernel - Re: [PATCH v2] irqchip/gic-v3-its: Allow GIC ITS number more than MAX

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Message-ID: <4e4c235c-c35c-10d8-8cb3-5a7ccad424b5@arm.com>
Date:   Wed, 26 Jul 2017 11:01:07 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Hanjun Guo <hanjun.guo@...aro.org>,
        Hanjun Guo <guohanjun@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-acpi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linuxarm@...wei.com,
        Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH v2] irqchip/gic-v3-its: Allow GIC ITS number more than
 MAX_NUMNODES

On 26/07/17 10:55, Hanjun Guo wrote:
> On 2017/7/26 16:00, Marc Zyngier wrote:
>> On 26/07/17 08:52, Hanjun Guo wrote:
>>> On 2017/7/25 18:30, Marc Zyngier wrote:
>>>> On 22/07/17 04:54, Hanjun Guo wrote:
>>>>> From: Hanjun Guo <hanjun.guo@...aro.org>
>>>>>
>>>>> When running 4.13-rc1 on top of D05, I got the boot log:
>>>>>
>>>>> [    0.000000] SRAT: PXM 0 -> ITS 0 -> Node 0
>>>>> [    0.000000] SRAT: PXM 0 -> ITS 1 -> Node 0
>>>>> [    0.000000] SRAT: PXM 0 -> ITS 2 -> Node 0
>>>>> [    0.000000] SRAT: PXM 1 -> ITS 3 -> Node 1
>>>>> [    0.000000] SRAT: ITS affinity exceeding max count[4]
>>>>>
>>>>> This is wrong on D05 as we have 8 ITSes with 4 NUMA nodes.
>>>>>
>>>>> So dynamically alloc the memory needed instead of using
>>>>> its_srat_maps[MAX_NUMNODES], which count the number of
>>>>> ITS entry(ies) in SRAT and alloc its_srat_maps as needed,
>>>>> then build the mapping of numa node to ITS ID. Of course,
>>>>> its_srat_maps will be freed after ITS probing because
>>>>> we don't need that after boot.
>>>>>
>>>>> After doing this, I got what I wanted:
>>>>>
>>>>> [    0.000000] SRAT: PXM 0 -> ITS 0 -> Node 0
>>>>> [    0.000000] SRAT: PXM 0 -> ITS 1 -> Node 0
>>>>> [    0.000000] SRAT: PXM 0 -> ITS 2 -> Node 0
>>>>> [    0.000000] SRAT: PXM 1 -> ITS 3 -> Node 1
>>>>> [    0.000000] SRAT: PXM 2 -> ITS 4 -> Node 2
>>>>> [    0.000000] SRAT: PXM 2 -> ITS 5 -> Node 2
>>>>> [    0.000000] SRAT: PXM 2 -> ITS 6 -> Node 2
>>>>> [    0.000000] SRAT: PXM 3 -> ITS 7 -> Node 3
>>>>>
>>>>> Fixes: dbd2b8267233 ("irqchip/gic-v3-its: Add ACPI NUMA node mapping")
>>>>> Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org>
>>>>> Cc: Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>
>>>>> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
>>>>> Cc: Marc Zyngier <marc.zyngier@....com>
>>>>> ---
>>>>>
>>>>> v1->v2:
>>>>>     - Add NULL check in acpi_get_its_numa_node() for no ITS affinity case;
>>>>>     - Free the its_srat_maps after ITS probing.
>>>>>
>>>>>    drivers/irqchip/irq-gic-v3-its.c | 39 ++++++++++++++++++++++++++++++++-------
>>>>>    1 file changed, 32 insertions(+), 7 deletions(-)
>>>>>
>>>>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>>>>> index 3ccdf76..1d692aa 100644
>>>>> --- a/drivers/irqchip/irq-gic-v3-its.c
>>>>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>>>>> @@ -1847,13 +1847,16 @@ struct its_srat_map {
>>>>>    	u32	its_id;
>>>>>    };
>>>>>    
>>>>> -static struct its_srat_map its_srat_maps[MAX_NUMNODES] __initdata;
>>>>> +static struct its_srat_map *its_srat_maps __initdata;
>>>>>    static int its_in_srat __initdata;
>>>>>    
>>>>>    static int __init acpi_get_its_numa_node(u32 its_id)
>>>>>    {
>>>>>    	int i;
>>>>>    
>>>>> +	if (!its_srat_maps)
>>>>> +		return NUMA_NO_NODE;
>>>>> +
>>>>>    	for (i = 0; i < its_in_srat; i++) {
>>>>>    		if (its_id == its_srat_maps[i].its_id)
>>>>>    			return its_srat_maps[i].numa_node;
>>>>> @@ -1861,6 +1864,12 @@ static int __init acpi_get_its_numa_node(u32 its_id)
>>>>>    	return NUMA_NO_NODE;
>>>>>    }
>>>>>    
>>>>> +static int __init gic_acpi_match_srat_its(struct acpi_subtable_header *header,
>>>>> +					  const unsigned long end)
>>>>> +{
>>>>> +	return 0;
>>>>> +}
>>>>> +
>>>>>    static int __init gic_acpi_parse_srat_its(struct acpi_subtable_header *header,
>>>>>    			 const unsigned long end)
>>>>>    {
>>>>> @@ -1877,12 +1886,6 @@ static int __init gic_acpi_parse_srat_its(struct acpi_subtable_header *header,
>>>>>    		return -EINVAL;
>>>>>    	}
>>>>>    
>>>>> -	if (its_in_srat >= MAX_NUMNODES) {
>>>>> -		pr_err("SRAT: ITS affinity exceeding max count[%d]\n",
>>>>> -				MAX_NUMNODES);
>>>>> -		return -EINVAL;
>>>>> -	}
>>>>> -
>>>>
>>>> So you're getting rid of that message when overflowing the array...
>>>
>>> This overflowing will not happen, because I scan the SRAT
>>> to count the entry(ies) of ITS affinity first to alloc the
>>> array, and then parse the same SRAT again to setup the mapping
>>> of NUMA node to ITS, so is it fine for us to just remove the
>>> check here?
>>
>> Removing that check is fine, as long as you make sure the allocation
>> hasn't failed.
> 
> Sorry, just want to make sure I understand correctly. This function will
> not be called if allocation failure, so do you mean we can keep the code
> as it is?

No. I mean adding this warning when the allocation fails, so that we
know that our NUMA topology is screwed.

	M.
-- 
Jazz is not dead. It just smells funny...