Messages in this thread | | | Date | Mon, 9 Jan 2012 21:33:17 +0530 | From | Vaidyanathan Srinivasan <> | Subject | Re: [PATCH] x86,sched: Fix sched_smt_power_savings totally broken |
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* Peter Zijlstra <peterz@infradead.org> [2012-01-09 15:35:07]:
> On Mon, 2012-01-09 at 16:30 +0530, Vaidyanathan Srinivasan wrote: > > Lets combine the MC/SMT options and create sched_powersavings={0,1,2} > > That will make it only one sysfs knob without any dependencies. > > > Is there really any sane rationale to keep the 1/2 thing? Why not have a > single boolean knob that says performance/power?
Yes, based on the architecture and topology, we do have two sweet spots for power vs performance trade offs. The first level should be to reduce power savings with marginal performance impact and second one will be to go for the most aggressive power savings.
The first one should generally be recommended as default to have a right balance between performance and power savings, while the second one should be used for reducing power consumption on unimportant workloads or under certain constraints.
Some example policies:
sched_powersavings=1:
Enable consolidation at MC level
sched_powersavings=2:
Enable aggressive consolidation at MC level and SMT level if available. In case arch can benefit from cross node consolidation, then enable it.
Having the above simple split in policy will enable wide adoption where the first level can be a recommended default. Having just a boolean enable/disable will mean the end-user will have to decide when to turn on and later off for best workload experience.
Just similar to cpufreq policy of performance, ondemand and powersave. They have their unique use cases and this design choice helps us ship ondemand as default.
--Vaidy
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