linux-kernel - Re: [PATCH 10/13] blk-mq: provide a default queue mapping for PCI device

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Date:   Mon, 19 Sep 2016 09:33:14 +0200
From:   Alexander Gordeev <agordeev@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     axboe@...com, tglx@...utronix.de, keith.busch@...el.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/13] blk-mq: provide a default queue mapping for PCI
 device

On Wed, Sep 14, 2016 at 04:18:56PM +0200, Christoph Hellwig wrote:
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  block/Makefile             |  2 +-
>  block/blk-mq-pci.c         | 45 +++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/blk-mq-pci.h |  9 +++++++++
>  3 files changed, 55 insertions(+), 1 deletion(-)
>  create mode 100644 block/blk-mq-pci.c
>  create mode 100644 include/linux/blk-mq-pci.h
> 
> diff --git a/block/Makefile b/block/Makefile
> index 9eda232..2447a0b 100644
> --- a/block/Makefile
> +++ b/block/Makefile
> @@ -22,4 +22,4 @@ obj-$(CONFIG_IOSCHED_CFQ)	+= cfq-iosched.o
>  obj-$(CONFIG_BLOCK_COMPAT)	+= compat_ioctl.o
>  obj-$(CONFIG_BLK_CMDLINE_PARSER)	+= cmdline-parser.o
>  obj-$(CONFIG_BLK_DEV_INTEGRITY) += bio-integrity.o blk-integrity.o t10-pi.o
> -
> +obj-$(CONFIG_PCI)		+= blk-mq-pci.o
> diff --git a/block/blk-mq-pci.c b/block/blk-mq-pci.c
> new file mode 100644
> index 0000000..33c7bd7
> --- /dev/null
> +++ b/block/blk-mq-pci.c
> @@ -0,0 +1,45 @@
> +/*
> + * Copyright (c) 2016 Christoph Hellwig.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + */
> +#include <linux/blk-mq.h>
> +#include <linux/blk-mq-pci.h>
> +#include <linux/pci.h>
> +#include <linux/module.h>
> +
> +/**
> + * blk_mq_pci_map_queues - provide a default queue mapping for PCI device
> + * @set:	tagset to provide the mapping for
> + * @pdev:	PCI device associated with @set.
> + *
> + * This function assumes the PCI device @pdev has at least as many available
> + * interrupt vetors as @set has queues.  It will then queuery the vector
> + * corresponding to each queue for it's affinity mask and built queue mapping
> + * that maps a queue to the CPUs that have irq affinity for the corresponding
> + * vector.
> + */
> +int blk_mq_pci_map_queues(struct blk_mq_tag_set *set, struct pci_dev *pdev)
> +{
> +	const struct cpumask *mask;
> +	unsigned int queue, cpu;
> +
> +	for (queue = 0; queue < set->nr_hw_queues; queue++) {
> +		mask = pci_irq_get_affinity(pdev, queue);
> +		if (!mask)
> +			return -EINVAL;
> +
> +		for_each_cpu(cpu, mask)
> +			set->mq_map[cpu] = queue;

Considering this code is to be used by any device - an assumption
that queue number and interrupt vector are always equal seems
questionable. I.e. what about non-contiguous MSI-Xs?

> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(blk_mq_pci_map_queues);
> diff --git a/include/linux/blk-mq-pci.h b/include/linux/blk-mq-pci.h
> new file mode 100644
> index 0000000..6ab5952
> --- /dev/null
> +++ b/include/linux/blk-mq-pci.h
> @@ -0,0 +1,9 @@
> +#ifndef _LINUX_BLK_MQ_PCI_H
> +#define _LINUX_BLK_MQ_PCI_H
> +
> +struct blk_mq_tag_set;
> +struct pci_dev;
> +
> +int blk_mq_pci_map_queues(struct blk_mq_tag_set *set, struct pci_dev *pdev);
> +
> +#endif /* _LINUX_BLK_MQ_PCI_H */
> -- 
> 2.1.4
>