Messages in this thread | | | Date | Thu, 26 Jun 2008 22:17:00 +0200 | From | Andi Kleen <> | Subject | Re: [RFC v1] Tunable sched_mc_power_savings=n |
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Vaidyanathan Srinivasan wrote:
Playing devil's advocate here.
> * Andi Kleen <andi@firstfloor.org> [2008-06-26 20:08:41]: > >>> A user could be an application and certain applications can predict their >>> workload. >> So you expect the applications to run suid root and change a sysctl? >> And what happens when two applications run that do that and they have differing >> requirements? Will they fight over the sysctl? > > System management software and workload monitoring and managing > software can potentially control the tunable on behalf of the > applications for best overall power savings and performance.
Does it have the needed information for that? e.g. real time information on what the system does? I don't think anybody is in a better position to control that than the kernel.
> Applications with conflicting goals should resolve among themselves.
That sounds wrong to me. Negotiating between conflicting requirements from different applications is something that kernels are supposed to do.
> The application with highest performance requirement should win.
That is right, but the kernel can do that based on nice levels and possibly other information, can't it?
> The > power QoS framework set_acceptable_latency() ensures that the lowest > latency set across the system wins.
But that only helps kernel drivers, not user space, doesn't it?
> Power management settings affect the entire system. It may not be > based on per application priority or nice value. However if the > priority of all the applications currently running in the system > indicate power savings, then the kernel can goto more aggressive power > saving state.
That's what I meant yes. So if only the file system indexer is running over night all niced it will run as power efficiently as possible.
> In a small-scale datacenters, peak and off-peak hour settings can be > potentially done through simple cron jobs.
Is there any real drawback from only controlling it through nice levels?
Anyways I think the main thing I object to in your proposal is that your tunable is system global, not per process. I'm also not sure if a tunable is really a good idea and if the kernel couldn't do a better job.
-Andi
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