linux-kernel - Re: [PATCH v5 5/7] iommu/dma: Allow a single FQ in addition to per-CPU FQs

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Message-ID: <Y9fy6KXdA3OqNudY@nvidia.com>
Date:   Mon, 30 Jan 2023 12:40:08 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Gerd Bayer <gbayer@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>, iommu@...ts.linux.dev,
        linux-s390@...r.kernel.org, borntraeger@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, linux-kernel@...r.kernel.org,
        Julian Ruess <julianr@...ux.ibm.com>
Subject: Re: [PATCH v5 5/7] iommu/dma: Allow a single FQ in addition to
 per-CPU FQs

On Mon, Jan 30, 2023 at 04:57:56PM +0100, Niklas Schnelle wrote:

> I'm wondering if maybe instead of plain flag bits it makes more sense
> to have a dma_iommu_options struct that contains the queue size and a
> flags value which indicates whether a single or per-CPU queue is
> used.

Querying the driver for what kind of performance tuning it would like
to use by default makes sense to me.

> Then I could add an iommu_ops callback that takes a device and a
> pointer to the dma_iommu_options. That way we can still set the options
> per device but don't need a whole extra domain type. This callback
> would then just be called during initialization of the DMA-FQ domain
> and not having the callback just leaves the defaults unchanged. Does
> that go in the right direction?

I like it

Jason