Need a program to measure CPU latency.

[Debian_SuperUser]

I am playing with my C-states on my Intel processor. Running in higher C-states should give me lower latency, but I want to know if the difference is even worth it, if there is a real difference at all, that too positive or negative difference. I tried Intel Memory Latency checker, but it is a memory latency test and I couldn't see any difference between different C-states at all. Then I tried core-latency from the Phoronix Test Suite. With normal C-states I will get 85 ns average, but with C-states disabled (running in C0 the full time), I actually got 90 ns. I need a different and better program that will test this latency better, and for knowledgeable people out there, if C-states even make any real difference to performance. They definitely do for power consumption though.

 

[CaffeineAddict]

Memory latency and C-states are two completely different things.
And CPU latency is the same thing as memory latency although that term is rather rarely used because there are several variables which define memory latency.

I tried Intel Memory Latency checker, but it is a memory latency test and I couldn't see any difference between different C-states at all.

Knowing the difference is essential to figure out why your question make not much sense and so can't achieve what you expect.

 

[Debian_SuperUser]

@CaffeineAddict

That's why I am looking for a program to test CPU latency in depth. In Intel MLC, it also tested the L2 to L2 cache hit latency between the cores. Really didn't make any difference at all. And as stated when I ran core latency test, I got higher latency when running in C0 only.

Tbh, if I didn't know about C-states, then I wouldn't have been bothered at all, just like I am starting to not being bothered slowly after trying to run these tests. Performance and latency just seem fine. But if it says that these deep C-states disable core cache and flush the cache to memory and sleep down a lot of the parts of the core, and waking them up back to C0 takes some latency and all, then I am a bit bothered, but I just can't see the difference in performance.

Also, running max frequency makes much more difference than running in highest C-state. I bench marked that as well.

 

[CaffeineAddict]

waking them up back to C0 takes some latency and all, then I am a bit bothered, but I just can't see the difference in performance.

Once you wake up your CPU it's doesn't save any power so it can't continue to affect latency.
C-states might be problem only if you expect normal latency while not having any intensive tasks running, like playing games.

C-states are to save power.
latency can't be improved software wise to a value grater than what's limited by RAM, you'd need better RAM for this and probably a new CPU and also mobo.

 

[Debian_SuperUser]

Once you wake up your CPU it's doesn't save any power so it can't continue to affect latency.

Yes but that is only when the CPU is running at 100% C0 residency. When doing normal tasks, it will always fluctuate a lot between C0 and C7 and in between.

Just let me know if you know or could find a program that can test CPU latency accurately. I will do the benchmarking myself and prove whats right or wrong.

 

[CaffeineAddict]

I don't know which program has this benchmark, maybe prime95.
In any case if C-states reduce latency just go to BIOS and disable them, problem solved.