Subject: Re: [PATCH v6 08/42] powerpc/powernv: Calculate PHB's DMA weight dynamically

From: Alexey Kardashevskiy <[email-masked]>
Date: Mon, 10 Aug 2015 19:21:12 +1000

On 08/06/2015 02:11 PM, Gavin Shan wrote:
> For P7IOC, the whole available DMA32 space, which is below the
> MEM32 space, is divided evenly into 256MB segments. The number
> of continuous segments assigned to one particular PE depends on
> the PE's DMA weight that is calculated based on the type of each
> PCI devices contained in the PE, and PHB's DMA weight which is
> accumulative DMA weight of PEs contained in the PHB. It means
> that the PHB's DMA weight calculation depends on existing PEs,
> which works perfectly now, but not hotplug friendly. As the
> whole available DMA32 space can be assigned to one PE on PHB3,
> so we don't have the issue on PHB3.
>
> The patch calculates PHB's DMA weight based on the PCI devices
> contained in the PHB dynamically so that it's hotplug friendly.
>
> Signed-off-by: Gavin Shan <[email-masked]>
> ---
>   arch/powerpc/platforms/powernv/pci-ioda.c | 88 +++++++++++++++----------------
>   arch/powerpc/platforms/powernv/pci.h      |  6 ---
>   2 files changed, 43 insertions(+), 51 deletions(-)
>
> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> index 713f4b4..7342cfd 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -927,6 +927,9 @@ static void pnv_ioda_link_pe_by_weight(struct pnv_phb *phb,
>
>   static unsigned int pnv_ioda_dma_weight(struct pci_dev *dev)
>   {
> +	struct pci_controller *hose = pci_bus_to_host(dev->bus);
> +	struct pnv_phb *phb = hose->private_data;
> +
>   	/* This is quite simplistic. The "base" weight of a device
>   	 * is 10. 0 means no DMA is to be accounted for it.
>   	 */
> @@ -939,14 +942,34 @@ static unsigned int pnv_ioda_dma_weight(struct pci_dev *dev)
>   	if (dev->class == PCI_CLASS_SERIAL_USB_UHCI ||
>   	    dev->class == PCI_CLASS_SERIAL_USB_OHCI ||
>   	    dev->class == PCI_CLASS_SERIAL_USB_EHCI)
> -		return 3;
> +		return 3 * phb->ioda.tce32_count;
>
>   	/* Increase the weight of RAID (includes Obsidian) */
>   	if ((dev->class >> 8) == PCI_CLASS_STORAGE_RAID)
> -		return 15;
> +		return 15 * phb->ioda.tce32_count;
>
>   	/* Default */
> -	return 10;
> +	return 10 * phb->ioda.tce32_count;
> +}
> +
> +static int __pnv_ioda_phb_dma_weight(struct pci_dev *pdev, void *data)
> +{
> +	unsigned int *dma_weight = data;
> +
> +	*dma_weight += pnv_ioda_dma_weight(pdev);
> +	return 0;
> +}
> +
> +static unsigned int pnv_ioda_phb_dma_weight(struct pnv_phb *phb)
> +{
> +	unsigned int dma_weight = 0;
> +
> +	if (!phb->hose->bus)
> +		return 0;
> +
> +	pci_walk_bus(phb->hose->bus,
> +		     __pnv_ioda_phb_dma_weight, &dma_weight);
> +	return dma_weight;
>   }
>
>   #ifdef CONFIG_PCI_IOV
> @@ -1097,14 +1120,6 @@ static void pnv_ioda_setup_bus_PE(struct pci_bus *bus, bool all)
>   	/* Put PE to the list */
>   	list_add_tail(&pe->list, &phb->ioda.pe_list);
>
> -	/* Account for one DMA PE if at least one DMA capable device exist
> -	 * below the bridge
> -	 */
> -	if (pe->dma_weight != 0) {
> -		phb->ioda.dma_weight += pe->dma_weight;
> -		phb->ioda.dma_pe_count++;
> -	}
> -
>   	/* Link the PE */
>   	pnv_ioda_link_pe_by_weight(phb, pe);
>   }
> @@ -2431,24 +2446,13 @@ static void pnv_pci_ioda2_setup_dma_pe(struct pnv_phb *phb,
>   static void pnv_ioda_setup_dma(struct pnv_phb *phb)
>   {
>   	struct pci_controller *hose = phb->hose;
> -	unsigned int residual, remaining, segs, tw, base;
>   	struct pnv_ioda_pe *pe;
> +	unsigned int dma_weight;
>
> -	/* If we have more PE# than segments available, hand out one
> -	 * per PE until we run out and let the rest fail. If not,
> -	 * then we assign at least one segment per PE, plus more based
> -	 * on the amount of devices under that PE
> -	 */
> -	if (phb->ioda.dma_pe_count > phb->ioda.tce32_count)
> -		residual = 0;
> -	else
> -		residual = phb->ioda.tce32_count -
> -			phb->ioda.dma_pe_count;
> -
> -	pr_info("PCI: Domain %04x has %ld available 32-bit DMA segments\n",
> -		hose->global_number, phb->ioda.tce32_count);
> -	pr_info("PCI: %d PE# for a total weight of %d\n",
> -		phb->ioda.dma_pe_count, phb->ioda.dma_weight);
> +	/* Calculate the PHB's DMA weight */
> +	dma_weight = pnv_ioda_phb_dma_weight(phb);
> +	pr_info("PCI%04x has %ld DMA32 segments, total weight %d\n",
> +		hose->global_number, phb->ioda.tce32_count, dma_weight);
>
>   	pnv_pci_ioda_setup_opal_tce_kill(phb);
>
> @@ -2456,22 +2460,9 @@ static void pnv_ioda_setup_dma(struct pnv_phb *phb)
>   	 * out one base segment plus any residual segments based on
>   	 * weight
>   	 */
> -	remaining = phb->ioda.tce32_count;
> -	tw = phb->ioda.dma_weight;
> -	base = 0;
>   	list_for_each_entry(pe, &phb->ioda.pe_dma_list, dma_link) {
>   		if (!pe->dma_weight)
>   			continue;
> -		if (!remaining) {
> -			pe_warn(pe, "No DMA32 resources available\n");
> -			continue;
> -		}
> -		segs = 1;
> -		if (residual) {
> -			segs += ((pe->dma_weight * residual)  + (tw / 2)) / tw;
> -			if (segs > remaining)
> -				segs = remaining;
> -		}
>
>   		/*
>   		 * For IODA2 compliant PHB3, we needn't care about the weight.
> @@ -2479,17 +2470,24 @@ static void pnv_ioda_setup_dma(struct pnv_phb *phb)
>   		 * the specific PE.
>   		 */
>   		if (phb->type == PNV_PHB_IODA1) {
> -			pe_info(pe, "DMA weight %d, assigned %d DMA32 segments\n",
> +			unsigned int segs, base = 0;
> +
> +			if (pe->dma_weight <
> +			    dma_weight / phb->ioda.tce32_count)
> +				segs = 1;
> +			else
> +				segs = (pe->dma_weight *
> +					phb->ioda.tce32_count) / dma_weight;
> +
> +			pe_info(pe, "DMA32 weight %d, assigned %d segments\n",
>   				pe->dma_weight, segs);
>   			pnv_pci_ioda_setup_dma_pe(phb, pe, base, segs);
> +
> +			base += segs;

This is not right. @base here is a local variable in the scope, 
pnv_pci_ioda_setup_dma_pe() will always be called with base==0.

Sorry for commenting the same patch twice.

>   		} else {
>   			pe_info(pe, "Assign DMA32 space\n");
> -			segs = 0;
>   			pnv_pci_ioda2_setup_dma_pe(phb, pe);
>   		}
> -
> -		remaining -= segs;
> -		base += segs;
>   	}
>   }
>
> diff --git a/arch/powerpc/platforms/powernv/pci.h b/arch/powerpc/platforms/powernv/pci.h
> index 08a4e57..addd3f7 100644
> --- a/arch/powerpc/platforms/powernv/pci.h
> +++ b/arch/powerpc/platforms/powernv/pci.h
> @@ -183,12 +183,6 @@ struct pnv_phb {
>   			/* 32-bit TCE tables allocation */
>   			unsigned long		tce32_count;
>
> -			/* Total "weight" for the sake of DMA resources
> -			 * allocation
> -			 */
> -			unsigned int		dma_weight;
> -			unsigned int		dma_pe_count;
> -
>   			/* Sorted list of used PE's, sorted at
>   			 * boot for resource allocation purposes
>   			 */
>

-- 
Alexey