linux-kernel - Re: [PATCH 4/5] nvme-pci: simplify nvme_setup_irqs() via .setup

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Date:   Mon, 11 Feb 2019 12:09:12 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Christoph Hellwig <hch@....de>, Bjorn Helgaas <helgaas@...nel.org>,
        Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH 4/5] nvme-pci: simplify nvme_setup_irqs() via
 .setup_affinity callback

On Sun, Feb 10, 2019 at 07:49:12PM +0100, Thomas Gleixner wrote:
> On Fri, 25 Jan 2019, Ming Lei wrote:
> > +static int nvme_setup_affinity(const struct irq_affinity *affd,
> > +			       struct irq_affinity_desc *masks,
> > +			       unsigned int nmasks)
> > +{
> > +	struct nvme_dev *dev = affd->priv;
> > +	int affvecs = nmasks - affd->pre_vectors - affd->post_vectors;
> > +	int curvec, usedvecs;
> > +	int i;
> > +
> > +	nvme_calc_io_queues(dev, nmasks);
> 
> So this is the only NVME specific information. Everything else can be done
> in generic code. So what you really want is:
> 
> 	struct affd {
> 		...
> +		calc_sets(struct affd *, unsigned int nvecs);
> 		...
> 	}
> 
> And sets want to be actually inside of the affinity descriptor structure:
> 
>         unsigned int num_sets;
> 	unsigned int set_vectors[MAX_SETS];
> 
> We surely can define a sensible maximum of sets for now. If that ever turns
> out to be insufficient, then struct affd might become to large for the
> stack, but for now, using e.g. 8, there is no need to do so.
> 
> So then the logic in the generic code becomes exactly the same as what you
> added to nvme_setup_affinity():
> 
> 	if (affd->calc_sets) {
> 		affd->calc_sets(affd, nvecs);
> 	} else if (!affd->num_sets) {
> 		affd->num_sets = 1;
> 		affd->set_vectors[0] = affvecs;
> 	}
> 
> 	for (i = 0; i < affd->num_sets; i++) {
> 	    ....
> 	}
> 
> See?

OK, will do this way in V2, then we can avoid drivers to abuse
the callback.

Thanks,
Ming