[coreboot] [PATCH] Add option 'compress ramstage'

[Scott Duplichan]

Sven Schnelle wrote:

]Add an option to make compression of ramstage configurable. Right now
]it is always compressed. On my Thinkpad, the complete boot to grub takes
]4s, with around 1s required for decompressing ramstage. This is probably
]caused by the fact the decompression does a lot of single byte/word/qword
]accesses, which are really slow on SPI buses. So give the user the option
]to store ramstage uncompressed, if he has enough memory.
]
]Signed-off-by: Sven Schnelle <svens at stackframe.org>

Hello Sven,

Thanks, I like having this option. For AMD Persimmon I get these
boot times for coreboot+seabios+dos ssd drive:

                                      Standard    No compress
SPI 33 MHz fast mode, prefetch        0.690       0.717
SPI 33 MHz fast mode, no prefetch     0.933       1.041
AMD Simnow                            9.0         3.0

For this project compress disable slows booting on real hardware slightly,
but it vastly improves simnow boot time.

Is your SB SPI prefetch enabled? Using the cycle logging feature of
DediProg EM100 shows that for AMD, SPI reads are all dwords until the
SB SPI prefetch is enabled, at which time they become cache line reads.

Thanks,
Scott