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An API for specifying latency constraints

An API for specifying latency constraints

Posted Aug 31, 2006 7:16 UTC (Thu) by ncm (subscriber, #165)
Parent article: An API for specifying latency constraints

I wonder how this can be transitioned in. It seems to me that any driver that doesn't declare its latency requirement must be assumed to need the minimum possible latency. The result is that the last driver to be updated holds up implementing power-down. It's not as bad as it might be, as lots of drivers aren't even open much of the time, and most of us won't have the hardware they drive, but I wonder how we will know which driver is keeping our own machine from sleeping.

The problem seems similar to discovering which daemon is keeping the disk from ever spinning down.

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An API for specifying latency constraints

Posted Aug 31, 2006 7:46 UTC (Thu) by arjan (subscriber, #36785) [Link]

Actually it's sort of the other way around. Right now, the power savings already happen, including the latency hit. It's just that these are right now blind to the actual requirements, and assume everything goes.

With this patch drivers and subsystems can put a brake on that behavior basically (which also means the power savings can be more agressive since they're less likely to run into bad behavior, but that's for a bit later).

Also, the good news is that for ALSA at least, the latency can be calculated in the subsystem; eg there is no need to adjust all sound drivers, just a few lines of code in the subsystem are enough... (the alsa patch is going to Andrew Morton today).

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