On Fri, Aug 15, 2014 at 10:37:32AM -0400, Ashwin Chaugule wrote: > Hi Peter, > > On 15 August 2014 10:07, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > 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. > > I think its still better than the "p-state" thing we have going today, > where the algorithms are making their decisions based on the incorrect > assumption that the CPU got what it requested for. (among other things > listed earlier.) CPPC at least gives you a guarantee that the > delivered performance will be within a range you requested. It can > even force the platform to deliver a specific performance value if you > choose over a specific time window. Maybe; the guarantee and interrupt on change might be useful indeed. But which ever way we need aperf/mperf ratios somewhere.
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