Jan Kiszka wrote:
The patch below adds infrastructure to track "maximum allowable
latency" for
power saving policies.
Very interesting approach. I wonder if it could be used to cover
another problematic source of latencies as well: asynchronous SMIs.
They quickly cause delays reaching from a few 100 us up to
milliseconds.
Hard-RT extension like Xenomai work around this on several Intel
chipsets by disabling SMI unconditionally
I would consider that a mistake. SMI's are used to do things like emergency thermal protections etc etc.
Disabling them unconditionally is going to risk you your hardware.
I guess an interface to let also applications / the sysadmin specifiy
a latency constraint would be useful as well. sysfs?
I thought about this a lot but decided against. There are already ways to do things like disable specific C states etc,
and if we expose this it'll mostly get abused by certain desktop applications who have no idea what they are doing ;=(
What makes anyone think that userspace could make a better decision than the drivers?
Video / Audio playback are not good examples since these both already would work automatically correct with only in-kernel
infrastructure. Hard-RT systems are also not a good example since those should use the existing boot parameters. I couldn't
come up with other scenarios, and until we have a good one I'm against exposing crap to sysfs "just because we can".
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