Proposal: [PATCH] Workaround for MPC5121 DTLB errata

[David Jander]

Please note: the proposed patch is actually incomplete, someone with better 
knowledge of PowerPC assembly than me should complete it.
According to the errata from Freescale, the proposed workaround should be a 
complete LRW (Least-Recently Written) implementation. AFAIK that would 
implicate holding an extra table in RAM with LRW information for each entry 
in the TLB.

Anyway, with this patch I am experiencing enormous speed-up overall. Some 
example tests I have done so far:

- 'mplayer -nosound -benchmark' shows a speedup of roughly 22 %

- 'prboom -timedemo test' (where 'test.lmb' is a prerecorded demo) shows an 
increase from 14.1 to 16.7 fps.

Sysnthetic memcpy() benchmarks may show a more drastic improvement (if they 
are hit by this bug):

Using 'minibench' from Gunnar Von Boehn, memcpy() speed goes up from 27Mbyte/s 
to 173Mbyte/s for memory-2-memory cases.

Greetings,

-- 
David Jander
Protonic Holland.