Performance of SheevaPlug on 8-stable

[Mark Tinguely]

	<deletes of my stuff>

>  > There are a few data dangling allocations that I would like to see
>  > closed from the multiple kernel allocation fix. *IN THEORY, IF* a page
>  > is allocated via the arm_nocache (DMA COHERENT) or a sendfile, then
>  > it is never marked as unallocated. *IN THEORY*, if that page is used
>  > again, then we could falsely believe that page is being shared and
>  > we turn off the cache, eventhough it is not shared.
>  > 
>  > 	http://www.casselton.net/~tinguely/arm_pmap_unmanaged.diff
>  > 
>  > * Disclaimer: I am not sure if DMA COHERENT nor sendfiles are used in
>  > the Sheeva implementation. This is a theoritical observation of a side
>  > effect of the multiple kernel mapping patch that we did just before
>  > FreeBSD 8-release.
>
>  I instrumented code with KTRs and your theory is correct. Kernel reuse page
>  which was previouly mapped via arm_nocache. Your patch should be applied
>  to -current.
>
>  grzesiek

Thank-you. I would appreciate it if someone would commit that patch. It
has been on my mind since FreeBSD 8.0-release. This patch should help some
data buffers because we do not incorrectly think this page is still mapped
to a KVA.

I don't think this our I/O performance problem solution, Off-list, I have
mentioned the belief that it may be beneficial to think of not turning
off the cache DMA_COHERENT even for ARMv4/ARMv5.

--Mark Tinguely.