Though, as a user of badly written drivers, I'm totally fucked. Its too bad the OS design does not allow for the user control any aspect of this (well apart from MaximumDpcQueueDepth).
- Typical driver dev: Knows nothing about DPC Importance Levels, and sticks with medium (default): IPIs are not sent to idle cores, so device experiences huge latencies as the DPC targeted to core 7 never, ever, gets delivered.
- Typical driver dev 2: Hears about this problem and learns that High/MediumHigh Importance DPCs cause an IPI to be delivered even to idle cores: wakes up every core in your system round-robin as part of his attempt to spread/reduce latencies, killing your battery life and causing IPI pollution.
Now I hear you saying: "But Alex, why not always target the DPC only to non-idle cores?". Yeah, if only the scheduler have you that kind of information in any sort of reliable way.
Really this is clearly the job of the OS. As it stands now, targeting DPCs on your own is a "fcked if you do, fcked if you don't" proposition.
You do get a few more variables you can play with as a user, but changing them will usually lead to worst problems than it would solve. Many drivers take dependencies on the default settings :/
Honestly.. I've spent countless hours hunting down bad drivers to fix audio stutter and other crap on my gaming PC. I've finally got DPC latency under 10microSec and I'm not touching a thing :)
It was just a simple example of something that could change for the better in terms of performance, but that probably won't because it's a significant amount of code churn with little $$$ benefit.
I was honestly surprised that a core-balancing algorithm was added in Windows 7, but that was done at the last second (RC2) and by a very senior (while young) dev that had a lot of balls and respect. Sadly he was thanked by being promoted into management, as is usual with Microsoft.