On Tue, 16 Oct 2012 12:50:22 -0700 Eric Anholt <eric at anholt.net> wrote: > It's not snarky, I'm really wondering if you've actually seen middle > frequencies like this software is designed to do. I spend a lot of time > looking at performance, and whenever I look at RPS state, it's either at > highest or lowest, or not working. I've never seen a functioning > workload that stays at the middle. Testing with the hsw values > reverted: Lemme step back here a minute too, since some people have had strong reactions to this proposal. My underlying assumption here is that we're not executing with as much power efficiency as we could. This is more the case with apps (desktop environments, non-gaming apps) that don't stress the GPU much, but may also be true for some games we can run faster than 60fps. In an ideal world, we'd run everything at the minimum frequency required to get it to whatever target framerate it has (60fps for games, 24fps or whatever for video, or some variable number for a compositor that has intermittent activity). We'd do that because even though we take more time to draw a frame, keeping the frequency low is more efficient from a power perspective, so over a given time period we end up consuming fewer joules than if we "race to idle" at the highest frequency. Unfortunately, achieving that ideal is difficult. Today's implementation doesn't take into account any fps target, and uses some sw programmed weight values to figure out when to trigger a frequency increase or decrease. The values we have today came from data collection done with the Windows driver, which uses a different gfx stack and has very different behavior from ours. We should probably tune them based on our own workloads, on a per-platform basis. But given that we don't give the hw any information about when we need things done or whether we're doing what we want to do, I thought we might be able to do better with some additional sw assistance. It's possible we could combine the proposal I sent out earlier (which boils down to userspace telling the kernel whether it's getting the performance it wants or not) with the hw-assisted mechanism, along with some additional tuning, or we could do something else entirely. Anyway, that's the background and I probably should have sent it out first. Jesse
