Messages in this thread | | | Date | Fri, 21 Dec 2012 22:10:19 -0500 | From | Konrad Rzeszutek Wilk <> | Subject | Re: [PATCH v7 24/27] x86: Add swiotlb force off support |
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On Fri, Dec 21, 2012 at 06:42:47PM -0800, Eric W. Biederman wrote: > Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> writes: > > > On Mon, Dec 17, 2012 at 11:15:56PM -0800, Yinghai Lu wrote: > >> So use could disable swiotlb from command line, even swiotlb support > >> is compiled in. Just like we have intel_iommu=on and intel_iommu=off. > > > > You really need to spell out why this is useful. > > YH why can't we safely autodetect that the swiotlb is unusable when > there is no memory below 4G free?
I am not sure what 'YH' stands for (Yeah?).
However we could turn SWIOTLB off altogether if it cannot allocate _some_ memory. It could try first 64MB, then 32MB, lastly 16MB. And if all that fails - print a nice warning and continue on.
Later in the late initialization phase, when pci_swiotlb_late_init is called - it can then figure out whether 'iommu' has been set and it iself was never able to allocate. At that point it can try the dynamic allocation (swiotlb_late_init_with_default_size) ... and if that fails give up and panic.
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