linux-kernel - Re: [PATCH 1/6] blk-mq: introduce blk_mq_hctx_map

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Message-ID: <20240913162654.GA713813@bhelgaas>
Date: Fri, 13 Sep 2024 11:26:54 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Daniel Wagner <wagi@...nel.org>
Cc: Jens Axboe <axboe@...nel.dk>, Bjorn Helgaas <bhelgaas@...gle.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	virtualization@...ts.linux.dev, linux-scsi@...r.kernel.org,
	megaraidlinux.pdl@...adcom.com, mpi3mr-linuxdrv.pdl@...adcom.com,
	MPT-FusionLinux.pdl@...adcom.com, storagedev@...rochip.com,
	linux-nvme@...ts.infradead.org, Daniel Wagner <dwagner@...e.de>,
	20240912-do-not-overwrite-pci-mapping-v1-1-85724b6cec49@...e.de,
	Ming Lei <ming.lei@...hat.com>
Subject: Re: [PATCH 1/6] blk-mq: introduce blk_mq_hctx_map_queues

On Fri, Sep 13, 2024 at 09:41:59AM +0200, Daniel Wagner wrote:
> From: Ming Lei <ming.lei@...hat.com>
> 
> blk_mq_pci_map_queues and blk_mq_virtio_map_queues will create a CPU to
> hardware queue mapping based on affinity information. These two
> function share code which only differs on how the affinity information
> is retrieved. Also there is the hisi_sas which open codes the same loop.
> 
> Thus introduce a new helper function for creating these mappings which
> takes an callback function for fetching the affinity mask. Also
> introduce common helper function for PCI and virtio devices to retrieve
> affinity masks.

> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index e3a49f66982d..84f9c16b813b 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -6370,6 +6370,26 @@ int pci_set_vga_state(struct pci_dev *dev, bool decode,
>  	return 0;
>  }
>  
> +#ifdef CONFIG_BLK_MQ_PCI
> +/**
> + * pci_get_blk_mq_affinity - get affinity mask queue mapping for PCI device
> + * @dev_data:	Pointer to struct pci_dev.
> + * @offset:	Offset to use for the pci irq vector
> + * @queue:	Queue index
> + *
> + * This function returns for a queue the affinity mask for a PCI device.
> + * It is usually used as callback for blk_mq_hctx_map_queues().
> + */
> +const struct cpumask *pci_get_blk_mq_affinity(void *dev_data, int offset,
> +					      int queue)
> +{
> +	struct pci_dev *pdev = dev_data;
> +
> +	return pci_irq_get_affinity(pdev, offset + queue);
> +}
> +EXPORT_SYMBOL_GPL(pci_get_blk_mq_affinity);
> +#endif

IMO this doesn't really fit well in drivers/pci since it doesn't add
any PCI-specific knowledge or require any PCI core internals, and the
parameters are blk-specific.  I don't object to the code, but it seems
like it could go somewhere in block/?

Bjorn