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by rz30221 1373 days ago
I read the article in full, and the data & information was interesting, but I have to say a lot of the points you're making in the comments now was not clear from the article text alone.

Another important point is you're measuring the default behavior of the various control systems. One can change that which would allow the user to observe something else.
1 comments
clamchowder 1373 days ago
Yeah, didn't want to start an article with a five paragraph essay especially when wordpress pagination doesn't work, so I can't get an Anandtech style multi-page article up.

And yep. You can even run a CPU at full clock all the time, meaning you will never observe a clock transition time. Cloud providers seem to do that.

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clamchowder 1373 days ago
Thanks :) I guess I can't reply to a 7th level comment, so hopefully this one shows up in the right place.

I agree, there are multiple factors at play. But I don't think it's basically an implementation choice. Certainly it looks like it in some cases (S821 on battery, HSW-E and SNB-E). But it doesn't seem to be the case elsewhere. For example, speed shift lowers clock transition time by taking the OS out of the control loop.

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bee_rider 1373 days ago
For some reason, this site hides the reply button after a certain reply-chain length, but you can just click on the person's name. This will show all their posts, including the one you want to reply to (you may have to look for it), with the reply buttons present.

I guess they must be trying to softly dis-incentivize really long chains, but not block them outright? It doesn't really make sense to me...

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sokoloff 1373 days ago
Faster is click on the timestamp of the post and you can reply directly in one click.
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rz30221 1373 days ago
I actually liked the article and I think the first image is really informative.

I guess my point is the "clock frequency ramp time" is really due to the interplay of a bunch of different control systems, some in the OS and some not. And when those systems get mixed together, in a somewhat uncontrolled way (which is the case for most PCs), a huge amount of variability is the result and that's what the article did a good job quantifying but IMHO didn't make clear.

But at the time scales in your plots "how quickly CPUs change clock speeds" is basically an implementation choice.

Just my $0.02

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