On Fri, Aug 15, 2014 at 09:08:50AM -0400, Ashwin Chaugule wrote:
If the OS only looks at Highest, Lowest, Delivered registers and only writes to Desired, then we're not really any different than how we do things today in the CPUFreq layer.
The thing is; we're already struggling to make 'sense' of x86 as it stands today. And it looks like this CPPC stuff makes the behaviour even less certain.
Or even in the case of intel_pstate, if you map Desired to PERF_CTL and get value of Delivered by using aperf/mperf ratios (as my experimental driver does), then we can still maintain the existing system performance. It seems like if an OS can make use of the additional information then it should be net win for overall power savings and performance enhancement. Also, using the CPPC descriptors, we should be able to have one driver across X86 and ARM64. (possibly others too.)
Yikes, so aaargh64 will go do creative power management too?
And worse; it will go do ACPI? Welcome to the world of guaranteed BIOS fail :-(