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SubjectRe: [patch V5 4/8] nvme-pci: Simplify interrupt allocation
On Fri, 15 Feb 2019, Marc Zyngier wrote:
> On Thu, 14 Feb 2019 20:47:59 +0000,
> Thomas Gleixner <tglx@linutronix.de> wrote:
> > drivers/nvme/host/pci.c | 108 ++++++++++++------------------------------------
> > 1 file changed, 28 insertions(+), 80 deletions(-)
> >
> > --- a/drivers/nvme/host/pci.c
> > +++ b/drivers/nvme/host/pci.c
> > @@ -2041,41 +2041,32 @@ static int nvme_setup_host_mem(struct nv
> > return ret;
> > }
> >
> > -/* irq_queues covers admin queue */
> > -static void nvme_calc_io_queues(struct nvme_dev *dev, unsigned int irq_queues)
> > +/*
> > + * nirqs is the number of interrupts available for write and read
> > + * queues. The core already reserved an interrupt for the admin queue.
> > + */
> > +static void nvme_calc_irq_sets(struct irq_affinity *affd, unsigned int nrirqs)
> > {
> > - unsigned int this_w_queues = write_queues;
> > -
> > - WARN_ON(!irq_queues);
> > -
> > - /*
> > - * Setup read/write queue split, assign admin queue one independent
> > - * irq vector if irq_queues is > 1.
> > - */
> > - if (irq_queues <= 2) {
> > - dev->io_queues[HCTX_TYPE_DEFAULT] = 1;
> > - dev->io_queues[HCTX_TYPE_READ] = 0;
> > - return;
> > - }
> > + struct nvme_dev *dev = affd->priv;
> > + unsigned int nr_read_queues;
> >
> > /*
> > - * If 'write_queues' is set, ensure it leaves room for at least
> > - * one read queue and one admin queue
> > - */
> > - if (this_w_queues >= irq_queues)
> > - this_w_queues = irq_queues - 2;
> > -
> > - /*
> > - * If 'write_queues' is set to zero, reads and writes will share
> > - * a queue set.
> > - */
> > - if (!this_w_queues) {
> > - dev->io_queues[HCTX_TYPE_DEFAULT] = irq_queues - 1;
> > - dev->io_queues[HCTX_TYPE_READ] = 0;
> > - } else {
> > - dev->io_queues[HCTX_TYPE_DEFAULT] = this_w_queues;
> > - dev->io_queues[HCTX_TYPE_READ] = irq_queues - this_w_queues - 1;
> > - }
> > + * If only one interrupt is available, combine write and read
> > + * queues. If 'write_queues' is set, ensure it leaves room for at
> > + * least one read queue.
>
> [Full disclaimer: I only have had two coffees this morning, and it is
> only at the fourth that my brain is able to kick in...]
>
> I don't know much about NVME, but I feel like there is a small
> disconnect between the code and the above comment, which says "leave
> room for at least one read queue"...
>
> > + */
> > + if (nrirqs == 1)
> > + nr_read_queues = 0;
> > + else if (write_queues >= nrirqs)
> > + nr_read_queues = nrirqs - 1;
>
> ... while this seem to ensure that we carve out one write queue out of
> the irq set. It looks like a departure from the original code, which
> would set nr_read_queues to 1 in that particular case.

Bah. right you are.

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