Re: [PATCH kernel v3 06/22] powerpc/powernv: Detach npu struct from pnv_phb

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 14/11/2018 15:28, Alistair Popple wrote:
> Hi Alexey,
> 
> On Tuesday, 13 November 2018 7:28:07 PM AEDT Alexey Kardashevskiy wrote:
>>  static struct npu *npdev_to_npu(struct pci_dev *npdev)
>>  {
>> -	struct pnv_phb *nphb;
>> +	struct pci_controller *hose = pci_bus_to_host(npdev->bus);
>> +	struct npu *npu;
>>
>> -	nphb = pci_bus_to_host(npdev->bus)->private_data;
>> +	list_for_each_entry(npu, &npu2_devices, next)
> 
> This is called from the ATSD path which is (or at least has been) quite a 
> performance critical path so searching through all the NPUs in a list may be 
> problematic.
> 
> I guess currently it wont make any practical difference as we only ever have 2 
> NPUs, but in future they may get divided into more logical NPUs. Would it be 
> possible to store a back-pointer somewhere so we can avoid the lookup?


It is quite possible even now with iommu_group_get() + container_of() +
iommu_group_put(), I'll try that in respin.


> 
>> +		if (hose == npu->hose)
>> +			return npu;
>>
>> -	return &nphb->npu;
>> +	WARN_ON_ONCE(1);
>> +	return NULL;
>>  }
>>
>>  /* Maximum number of nvlinks per npu */
>> @@ -505,6 +531,9 @@ static void acquire_atsd_reg(struct npu_context
>> *npu_context, continue;
>>
>>  			npu = npdev_to_npu(npdev);
>> +			if (!npu)
>> +				continue;
>> +
>>  			mmio_atsd_reg[i].npu = npu;
>>  			mmio_atsd_reg[i].reg = get_mmio_atsd_reg(npu);
>>  			while (mmio_atsd_reg[i].reg < 0) {
>> @@ -701,6 +730,8 @@ struct npu_context *pnv_npu2_init_context(struct pci_dev
>> *gpdev,
>>
>>  	nphb = pci_bus_to_host(npdev->bus)->private_data;
>>  	npu = npdev_to_npu(npdev);
>> +	if (!npu)
>> +		return ERR_PTR(-ENODEV);
>>
>>  	/*
>>  	 * Setup the NPU context table for a particular GPU. These need to be
>> @@ -821,6 +852,8 @@ void pnv_npu2_destroy_context(struct npu_context
>> *npu_context,
>>
>>  	nphb = pci_bus_to_host(npdev->bus)->private_data;
>>  	npu = npdev_to_npu(npdev);
>> +	if (!npu)
>> +		return;
>>  	nvlink_dn = of_parse_phandle(npdev->dev.of_node, "ibm,nvlink", 0);
>>  	if (WARN_ON(of_property_read_u32(nvlink_dn, "ibm,npu-link-index",
>>  							&nvlink_index)))
>> @@ -898,9 +931,15 @@ int pnv_npu2_init(struct pnv_phb *phb)
>>  	struct pci_dev *gpdev;
>>  	static int npu_index;
>>  	uint64_t rc = 0;
>> +	struct pci_controller *hose = phb->hose;
>> +	struct npu *npu;
>> +	int ret;
>>
>> -	phb->npu.nmmu_flush =
>> -		of_property_read_bool(phb->hose->dn, "ibm,nmmu-flush");
>> +	npu = kzalloc(sizeof(*npu), GFP_KERNEL);
>> +	if (!npu)
>> +		return -ENOMEM;
>> +
>> +	npu->nmmu_flush = of_property_read_bool(hose->dn, "ibm,nmmu-flush");
>>  	for_each_child_of_node(phb->hose->dn, dn) {
>>  		gpdev = pnv_pci_get_gpu_dev(get_pci_dev(dn));
>>  		if (gpdev) {
>> @@ -914,18 +953,31 @@ int pnv_npu2_init(struct pnv_phb *phb)
>>  		}
>>  	}
>>
>> -	for (i = 0; !of_property_read_u64_index(phb->hose->dn, "ibm,mmio-atsd",
>> +	for (i = 0; !of_property_read_u64_index(hose->dn, "ibm,mmio-atsd",
>>  							i, &mmio_atsd); i++)
>> -		phb->npu.mmio_atsd_regs[i] = ioremap(mmio_atsd, 32);
>> +		npu->mmio_atsd_regs[i] = ioremap(mmio_atsd, 32);
>>
>> -	pr_info("NPU%lld: Found %d MMIO ATSD registers", phb->opal_id, i);
>> -	phb->npu.mmio_atsd_count = i;
>> -	phb->npu.mmio_atsd_usage = 0;
>> +	pr_info("NPU%d: Found %d MMIO ATSD registers", hose->global_number, i);
>> +	npu->mmio_atsd_count = i;
>> +	npu->mmio_atsd_usage = 0;
>>  	npu_index++;
>> -	if (WARN_ON(npu_index >= NV_MAX_NPUS))
>> -		return -ENOSPC;
>> +	if (WARN_ON(npu_index >= NV_MAX_NPUS)) {
>> +		ret = -ENOSPC;
>> +		goto fail_exit;
>> +	}
>>  	max_npu2_index = npu_index;
>> -	phb->npu.index = npu_index;
>> +	npu->index = npu_index;
>> +	npu->hose = hose;
>> +
>> +	list_add(&npu->next, &npu2_devices);
> 
> Guess we don't need any locking here as the list gets setup once during boot 
> long before loading the driver and is never modified right?


Correct.


> 
> - Alistair
> 
>>  	return 0;
>> +
>> +fail_exit:
>> +	for (i = 0; i < npu->mmio_atsd_count; ++i)
>> +		iounmap(npu->mmio_atsd_regs[i]);
>> +
>> +	kfree(npu);
>> +
>> +	return ret;
>>  }
> 
> 

-- 
Alexey