[Libre-soc-bugs] [Bug 238] POWER Compressed Formal Standard writeup

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Sun Nov 15 19:15:13 GMT 2020


--- Comment #11 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to cand from comment #10)
> I feel paging would be too inflexible, unless it was configurable at
> runtime. And that is both plain crazy, and interesting given LTO. Gcc could
> link-time-optimize the whole program, figure out it uses less than 1024
> instructions, and create a custom page loaded at startup.

that was, from what i understand, partly the intent of transmeta.

the compromise is instead to analyse certain computationally-intensive
workloads.  yet with different tasks if we do _not_ have banks optimised
for specific tasks and workloads, *all* tasks and workloads are penalised
as a result.

that in turn loses us the opportunity to reduce cache size or usage,
which in turn pushes up power consumption.

Western Digital showed that even a small change of adding the most
commonly-used instructions that were used for *their* workload (HDD/SSD
workload), they got a huge extra compression ratio in program size.

that was only 4-5 instructions that resulted in something like a massive
10% program size reduction over and above what RVC already provides.

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