Messages in this thread | | | Date | Mon, 22 Sep 2008 21:01:44 +0200 | From | Joerg Roedel <> | Subject | Re: [PATCH] remove fullflush and nofullflush in IOMMU generic option |
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On Mon, Sep 22, 2008 at 08:48:22PM +0200, Ingo Molnar wrote: > applied Fujita's patch below to tip/x86/iommu that reverts those > options, thanks guys! > > i'm wondering how we should proceed. For debug, iommu=off is certainly > good enough - all kernels are supposed to work out of box on all hw, and > every other result is a regression that must be fixed. > > For performance tuning, it probably makes sense for developers to tune > IOMMU details (so that the bootup defaults can be improved - this is not > really something that should be done on a workload basis), but for that > IMO a /debug interface is a lot more useful than rather intrusive (and > inflexible) boot options. > > What do you think about a debugfs based tuning of various IOMMU details? > Maybe even the active driver could be changed - say from AMD-IOMMU to > GART, or to off.
Yes, for the IO/TLB flushing policy a /debug interface is usefull and certainly for a number of other parameters we have today at the commandline. But I am not sure if we can change the IOMMU implementation on-the-fly at runtime. We have to wait until all drivers have released their dma memory before we can switch it off. For coherent allocations this may take a long time. So for selecting the type of IOMMU active in the system the command line parameters are needed, I think. I prefer the iommu=$type parameter for selecting the default (better: to select a default different from what the kernel had chosen itself). We can have the IOMMU specific options to switch it off in addition if we like to.
Joerg
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