this change is to improve concurrency:
- Drop global state stored in the shadow overflow page table (and all other
global state)
- Remove all global locks
- Use per-PTE lock bits to allow parallel page insertion
- Reconstruct state when requested for evicted PTEs instead of buffering
it during overflow
This drops total wall time for make buildworld on a 32-thread POWER8 system
by a factor of two and system time by a factor of three, providing performance
20% better than similarly clocked Core i7 Xeons per-core. Performance on
smaller SMP systems, where PMAP lock contention was not as much of an issue,
is nearly unchanged.
Tested on: POWER8, POWER5+, G5 UP, G5 SMP (64-bit and 32-bit kernels)
Merged from: user/nwhitehorn/ppc64-pmap-rework
Looked over by: jhibbits, andreast
MFC after: 3 months
Relnotes: yes
Sponsored by: FreeBSD Foundation
available on firmwares 3.15 and earlier.
Caveats: Support for the internal SATA controller is currently missing,
as is support for framebuffer resolutions other than 720x480. These
deficiencies will be remedied soon.
Special thanks to Peter Grehan for providing the hardware that made this
port possible, and thanks to Geoff Levand of Sony Computer Entertainment
for advice on the LV1 hypervisor.
