Comment by wruza | Hacker News Reader

Comment by wruza | Hacker News Reader

missing vblank due to power management

Ugh. Few years ago I've built a gaming rig with i5-8400 and GTX1080 (both chosen for known workloads). Some games ran fine, but some were jerky af, and frametime monitor was zigzag-y all over the place. I thought that maybe 8400 was not a best choice despite my research and bought i7-8700 only to see that situation got much worse. After days of googling and discussions I found the issue: mobo bios had C1E state enabled. In short, it allows to drop the CPU frequency and voltage significantly when it's idling, but this technique isn't ready to operate 100+ times per second. After drawing a frame, CPU basically did nothing for a period of time (<10ms), which was enough to drop to C1E, but it can't get out of it quickly for some reason. And of course 8700 was much better at sucking at it, since it had more free time to fall asleep.

I understand that power saving is useful in general, but man, when Direct3D sees every other frame skipped, maybe it's time to turn the damn thing off for a while. Idk how a regular consumer could deal with it. You basically spend a little fortune on a rig, which then stutters worse than an average IGP because of some stupid misconfiguration.

> but it can't get out of it quickly for some reason

As overclockers are aware, to achieve higher frequencies but keep CPU stable, one gonna need higher CPU voltage. Works other way too, lowing frequency allows to lower voltage, and that’s what mostly delivers the power saving from these low-power states.

These chips can’t adjust voltage instantly because wires inside them are rather thin, and there’s non-trivial capacity everywhere. This means CPUs can drop frequency instantly, then decrease the voltage over time. However, if they raise frequency instantly without first raising the voltage, the chip will glitch.

That’s AFAIK the main reason why increasing the clock frequency takes time. The chips first raise the voltage which takes time because capacity, and only then they can raise the frequency which is instant.

There's apps that disable C states and core parking, and boost P states.

I use QuickCPU and max everything out. Yes it sounds like a sham but works wonders.

https://coderbag.com/product/quickcpu

I simply disabled C1E in BIOS, because it's a desktop. But still had to use EmptyStandbyList technique afterwards, which helps with the rest of the issue (tested with and without for few days, it really works).

I also recommend scheduling an ESL task.

What does ESL mean in this context? Google isn't particularly helpful on this one.

EmptyStandbyList. I fell into the same trap as you and tried searching 'ESL Task', but it's in the post they were responding to.

I strongly agree with you, and it's just that I have i7, but all of the experiences are quite similar.

Reply on news.ycombinator.com