Messages in this thread | | | From | Andy Lutomirski <> | Date | Wed, 4 Dec 2019 09:57:41 -0800 | Subject | Re: Running an Ivy Bridge cpu at fixed frequency |
| |
On Wed, Dec 4, 2019 at 9:01 AM David Laight <David.Laight@aculab.com> wrote: > > Is there any way to persuade the intel_pstate driver to make an Ivy bridge (i7-3770) > cpu run at a fixed frequency? > It is really difficult to compare code execution times when the cpu clock speed > keeps changing. > I thought I'd managed by setting the 'scaling_max_freq' to 1.7GHz, but even that > doesn't seem to be working now. > It would also be nice to run a little faster than that - but without it 'randomly' > going to 'turbo' frequencies (which it is doing even after I've set no_turbo to 1). >
I don't remember. I'm sure I could figure out what MSR to write, but that's not the answer you're looking for. Someone else will know :)
> An alternative would be a variable frequency TSC - might give more consistent values.
You can quite easily use perf to count cycles. I never really finished it, but this is a tiny little library that should do exactly what you need. It's a bit messy.
https://git.kernel.org/pub/scm/linux/kernel/git/luto/misc-tests.git/tree/tight_loop/perf_self_monitor.c
| |