Re: [PATCH] quiet down swiotlb warnings

[Andi Kleen <andi@firstfloor.org>]

Rik van Riel <riel@redhat.com> 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?

>  	 */
> -	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.

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. 

 -Andi