ppcmmu: Track translated entries for invalidation - #219
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PAT generation counters make invalidation constant-time by adding a generation check to every TLB lookup, but they added a per-access overhead to compare generation counters. I am swithcing to an alternate approach (explicitly tracking populated entries, which can also be used for BAT-derived entries), and am removing this first to make that diff easier to read. This logically reverts the work from dingusdev#199 (the TLB helper refactoring from dingusdev#203 prevents a mechanical revert).
XNU frequently changes BAT and PAT mappings for physical-memory access. Each resulting context synchronization can walk tens of thousands of TLB entries, which consumes a lot of time. Record the instruction and data TLB slots populated by BAT or PAT and invalidate only those slots. Pending invalidations are coalesced by source, and BAT updates cover PAT-derived entries because a new BAT can shadow a page mapping. Saves another 0.7 secondss in the time it takes to boot Mac OS X 10.3 to the WindowServer (compared to the generational PAT invalidation).
Avoids unncessary TLB invalidations.
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XNU frequently changes BAT and PAT mappings for physical-memory access. Each resulting context synchronization can walk tens of thousands of TLB entries, which consumes a lot of time.
Record the instruction and data TLB slots populated by BAT or PAT and invalidate only those slots. Pending invalidations are coalesced by source. This supersedes the PAT generational counter optimization from #199 - there are fewer BAT changes after boot, and having the overhead of a generation check on every TLB entry access would have made everything slower.
Also includes an additional optimization skip over no-op BAT writes.
Saves another 0.7 seconds in the time it takes to boot Mac OS X 10.3 to the WindowServer.