Re: [RFC PATCH v4 08/38] NTB: epf: Provide db_vector_count/db_vector_mask callbacks

On Sun, Jan 18, 2026 at 10:54:10PM +0900, Koichiro Den wrote:
> Provide db_vector_count() and db_vector_mask() implementations for both
> ntb_hw_epf and pci-epf-vntb so that ntb_transport can map MSI vectors to
> doorbell bits. Without them, the upper layer cannot identify which
> doorbell vector fired and ends up scheduling rxc_db_work() for all queue
> pairs, resulting in a thundering-herd effect when multiple queue pairs
> (QPs) are enabled.
>
> With this change, .peer_db_set() must honor the db_bits mask and raise
> all requested doorbell interrupts, so update those implementations
> accordingly.
>
> Signed-off-by: Koichiro Den <[email protected]>
> ---

Patch 6/7/8 can be post seperatly. Basic look good.

Frank

>  drivers/ntb/hw/epf/ntb_hw_epf.c               | 47 ++++++++++++-------
>  drivers/pci/endpoint/functions/pci-epf-vntb.c | 41 +++++++++++++---
>  2 files changed, 64 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
> index dbb5bebe63a5..c37ede4063dc 100644
> --- a/drivers/ntb/hw/epf/ntb_hw_epf.c
> +++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
> @@ -381,7 +381,7 @@ static int ntb_epf_init_isr(struct ntb_epf_dev *ndev, int msi_min, int msi_max)
>  		}
>  	}
>
> -	ndev->db_count = irq;
> +	ndev->db_count = irq - 1;
>
>  	ret = ntb_epf_send_command(ndev, CMD_CONFIGURE_DOORBELL,
>  				   argument | irq);
> @@ -415,6 +415,22 @@ static u64 ntb_epf_db_valid_mask(struct ntb_dev *ntb)
>  	return ntb_ndev(ntb)->db_valid_mask;
>  }
>
> +static int ntb_epf_db_vector_count(struct ntb_dev *ntb)
> +{
> +	return ntb_ndev(ntb)->db_count;
> +}
> +
> +static u64 ntb_epf_db_vector_mask(struct ntb_dev *ntb, int db_vector)
> +{
> +	struct ntb_epf_dev *ndev = ntb_ndev(ntb);
> +
> +	db_vector--; /* vector 0 is reserved for link events */
> +	if (db_vector < 0 || db_vector >= ndev->db_count)
> +		return 0;
> +
> +	return ndev->db_valid_mask & BIT_ULL(db_vector);
> +}
> +
>  static int ntb_epf_db_set_mask(struct ntb_dev *ntb, u64 db_bits)
>  {
>  	return 0;
> @@ -507,26 +523,21 @@ static int ntb_epf_peer_mw_get_addr(struct ntb_dev *ntb, int idx,
>  static int ntb_epf_peer_db_set(struct ntb_dev *ntb, u64 db_bits)
>  {
>  	struct ntb_epf_dev *ndev = ntb_ndev(ntb);
> -	u32 interrupt_num = ffs(db_bits) + 1;
> -	struct device *dev = ndev->dev;
> +	u32 interrupt_num;
>  	u32 db_entry_size;
>  	u32 db_offset;
>  	u32 db_data;
> -
> -	if (interrupt_num >= ndev->db_count) {
> -		dev_err(dev, "DB interrupt %d greater than Max Supported %d\n",
> -			interrupt_num, ndev->db_count);
> -		return -EINVAL;
> -	}
> +	unsigned long i;
>
>  	db_entry_size = readl(ndev->ctrl_reg + NTB_EPF_DB_ENTRY_SIZE);
>
> -	db_data = readl(ndev->ctrl_reg + NTB_EPF_DB_DATA(interrupt_num));
> -	db_offset = readl(ndev->ctrl_reg + NTB_EPF_DB_OFFSET(interrupt_num));
> -
> -	writel(db_data, ndev->db_reg + (db_entry_size * interrupt_num) +
> -	       db_offset);
> -
> +	for_each_set_bit(i, (unsigned long *)&db_bits, ndev->db_count) {
> +		interrupt_num = i + 1;
> +		db_data = readl(ndev->ctrl_reg + NTB_EPF_DB_DATA(interrupt_num));
> +		db_offset = readl(ndev->ctrl_reg + NTB_EPF_DB_OFFSET(interrupt_num));
> +		writel(db_data, ndev->db_reg + (db_entry_size * interrupt_num) +
> +		       db_offset);
> +	}
>  	return 0;
>  }
>
> @@ -556,6 +567,8 @@ static const struct ntb_dev_ops ntb_epf_ops = {
>  	.spad_count		= ntb_epf_spad_count,
>  	.peer_mw_count		= ntb_epf_peer_mw_count,
>  	.db_valid_mask		= ntb_epf_db_valid_mask,
> +	.db_vector_count	= ntb_epf_db_vector_count,
> +	.db_vector_mask		= ntb_epf_db_vector_mask,
>  	.db_set_mask		= ntb_epf_db_set_mask,
>  	.mw_set_trans		= ntb_epf_mw_set_trans,
>  	.mw_clear_trans		= ntb_epf_mw_clear_trans,
> @@ -607,8 +620,8 @@ static int ntb_epf_init_dev(struct ntb_epf_dev *ndev)
>  	int ret;
>
>  	/* One Link interrupt and rest doorbell interrupt */
> -	ret = ntb_epf_init_isr(ndev, NTB_EPF_MIN_DB_COUNT + NTB_EPF_IRQ_RESERVE,
> -			       NTB_EPF_MAX_DB_COUNT + NTB_EPF_IRQ_RESERVE);
> +	ret = ntb_epf_init_isr(ndev, NTB_EPF_MIN_DB_COUNT + 1 + NTB_EPF_IRQ_RESERVE,
> +			       NTB_EPF_MAX_DB_COUNT + 1 + NTB_EPF_IRQ_RESERVE);
>  	if (ret) {
>  		dev_err(dev, "Failed to init ISR\n");
>  		return ret;
> diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> index 4927faa28255..39e784e21236 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> @@ -1384,6 +1384,22 @@ static u64 vntb_epf_db_valid_mask(struct ntb_dev *ntb)
>  	return BIT_ULL(ntb_ndev(ntb)->db_count) - 1;
>  }
>
> +static int vntb_epf_db_vector_count(struct ntb_dev *ntb)
> +{
> +	return ntb_ndev(ntb)->db_count;
> +}
> +
> +static u64 vntb_epf_db_vector_mask(struct ntb_dev *ntb, int db_vector)
> +{
> +	struct epf_ntb *ndev = ntb_ndev(ntb);
> +
> +	db_vector--; /* vector 0 is reserved for link events */
> +	if (db_vector < 0 || db_vector >= ndev->db_count)
> +		return 0;
> +
> +	return BIT_ULL(db_vector);
> +}
> +
>  static int vntb_epf_db_set_mask(struct ntb_dev *ntb, u64 db_bits)
>  {
>  	return 0;
> @@ -1487,20 +1503,29 @@ static int vntb_epf_peer_spad_write(struct ntb_dev *ndev, int pidx, int idx, u32
>
>  static int vntb_epf_peer_db_set(struct ntb_dev *ndev, u64 db_bits)
>  {
> -	u32 interrupt_num = ffs(db_bits) + 1;
>  	struct epf_ntb *ntb = ntb_ndev(ndev);
>  	u8 func_no, vfunc_no;
> -	int ret;
> +	u64 failed = 0;
> +	unsigned long i;
>
>  	func_no = ntb->epf->func_no;
>  	vfunc_no = ntb->epf->vfunc_no;
>
> -	ret = pci_epc_raise_irq(ntb->epf->epc, func_no, vfunc_no,
> -				PCI_IRQ_MSI, interrupt_num + 1);
> -	if (ret)
> -		dev_err(&ntb->ntb->dev, "Failed to raise IRQ\n");
> +	for_each_set_bit(i, (unsigned long *)&db_bits, ntb->db_count) {
> +		/*
> +		 * DB bit i is MSI interrupt (i + 2).
> +		 * Vector 0 is used for link events and MSI vectors are
> +		 * 1-based for pci_epc_raise_irq().
> +		 */
> +		if (pci_epc_raise_irq(ntb->epf->epc, func_no, vfunc_no,
> +				      PCI_IRQ_MSI, i + 2))
> +			failed |= BIT_ULL(i);
> +	}
> +	if (failed)
> +		dev_err(&ntb->ntb->dev, "Failed to raise IRQ (%#llx)\n",
> +			failed);
>
> -	return ret;
> +	return failed ? -EIO : 0;
>  }
>
>  static u64 vntb_epf_db_read(struct ntb_dev *ndev)
> @@ -1561,6 +1586,8 @@ static const struct ntb_dev_ops vntb_epf_ops = {
>  	.spad_count		= vntb_epf_spad_count,
>  	.peer_mw_count		= vntb_epf_peer_mw_count,
>  	.db_valid_mask		= vntb_epf_db_valid_mask,
> +	.db_vector_count	= vntb_epf_db_vector_count,
> +	.db_vector_mask		= vntb_epf_db_vector_mask,
>  	.db_set_mask		= vntb_epf_db_set_mask,
>  	.mw_set_trans		= vntb_epf_mw_set_trans,
>  	.mw_clear_trans		= vntb_epf_mw_clear_trans,
> --
> 2.51.0
>