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    SubjectRe: [PATCH] quiet down swiotlb warnings
    On Fri, 01 Jun 2007, Andi Kleen wrote:

    > Rik van Riel <> writes:
    > > It turns out that the qla2xxx driver sometimes fills up the iotlb
    > > on purpose and throttles itself when pci_map_sg() fails. In the
    > > case of a driver that expects and handles pci_map_sg() failures,
    > > we should not spam the user's console with swiotlb full messages.
    > Why does it do that? Could we supply a better interface
    > for whatever it is trying to do here?

    The driver only calls pci_map_sg() once it's insured that all local
    driver resources are available to submit an I/O to the hardware.

    > > - printk(KERN_ERR "DMA: Out of SW-IOMMU space for %zu bytes at "
    > > - "device %s\n", size, dev ? dev->bus_id : "?");
    > > + if (++warnings < 5)
    > > + printk(KERN_ERR "DMA: Out of SW-IOMMU space for %zu bytes at "
    > > + "device %s\n", size, dev ? dev->bus_id : "?");
    > Bad idea imho. swiotlb mappings should always lead to printk by default
    > because it is pretty dangerous.

    Why? It's just another resource which is consumed -- the qla2xxx
    driver is the final consumer before I/O is submitted out on the wire.
    The mappings are held for the shorted time required -- as such, are
    released as soon as the I/O completes.

    > One possible solution for this I could think of would be to define a
    > new pci_map_sg_couldfail() or similar that doesn't warn and use a weak
    > fallback just calling pci_map_sg on other IOMMU implementations.
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      Last update: 2007-06-01 20:19    [W:0.022 / U:7.440 seconds]
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