Messages in this thread | | | Date | Wed, 08 Oct 2014 14:36:49 -0700 | From | "H. Peter Anvin" <> | Subject | Re: i915.ko WC writes are slow after ea8596bb2d8d379 |
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On 10/08/2014 12:49 PM, Chris Wilson wrote: > > Indeed, this appears to be the explanation. (And here I thought PAT > superseded mtrrs - i915.ko stopped trying to use assign an mtrr for its > GTT quite a while ago.) > > Replacing the stop_machine there with on_each_cpu does the trick: >
It should, but there seem to be quite a few drivers which still muck with MTRRs. However, i915 is not one of them, it calls io_mapping_create_wc() followed by arch_phys_wc_add(), so I'm wondering what the heck is going on here.
> Naively I would say that we lost the wc on our ioremap. > /sys/kernel/debug/x86/pat_memtype_list remained the same across repeated > runs.
Could you tell me what the above looks like?
-hpa
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