Messages in this thread |  | | Date | Mon, 31 Mar 2008 09:55:20 +0200 | From | Thomas Hellström <> | Subject | Re: [PATCH] x86: create array based interface to change page attribute |
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Andi Kleen wrote: > Dave Airlie <airlied@redhat.com> writes: > >> >> +#define CPA_FLUSHTLB 1 >> +#define CPA_ARRAY 2 >> > > I don't think CPA_ARRAY should be a separate case. Rather single > page flushing should be an array with only a single entry. pageattr > is already very complex, no need to make add more special cases. > >> + >> + /* >> + * Only flush present addresses: >> + */ >> + if (pte && (pte_val(*pte) & _PAGE_PRESENT)) >> + clflush_cache_range((void *) *addr, PAGE_SIZE); >> > > Also it is doubtful clflush really makes sense on a large array. Just > doing wbinvd might be faster then. Or perhaps better supporting Self-Snoop > should be revisited, that would at least eliminate it on most Intel > CPUs. > > I agree that wbinvd() seems to be faster on large arrays on the processors I've tested. But isn't there a severe latency problem with that instruction, that makes people really want to avoid it in all possible cases?
Also I think we need to clarify the semantics of the c_p_a functionality. Right now both AGP and DRM relies on c_p_a doing an explicit cache flush. Otherwise the data won't appear on the device side of the aperture. If we use self-snoop, the AGP and DRM drivers can't rely on this flush being performed, and they have to do the flush themselves, and for non-self-snooping processors, the flush needs to be done twice?
/Thomas
> -Andi >
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