this post was submitted on 28 Aug 2023
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[–] [email protected] 9 points 1 year ago* (last edited 1 year ago) (1 children)

It's not just random, it simply does not even work. Because they set this:

+/*Preferred Core featue is supported*/
+static bool prefcore = true;

And later in the code they do the if condition wrong:

+	if (prefcore)
+		WRITE_ONCE(cpudata->highest_perf, AMD_PSTATE_PREFCORE_THRESHOLD);
+	else
+		WRITE_ONCE(cpudata->highest_perf, AMD_CPPC_HIGHEST_PERF(cap1));

if should look like this:

+	if (prefcore)
+		WRITE_ONCE(cpudata->highest_perf, AMD_CPPC_HIGHEST_PERF(cap1));
+	else
+		WRITE_ONCE(cpudata->highest_perf, AMD_PSTATE_PREFCORE_THRESHOLD);

There is probably even more wrong, looking at the code quality, but this at least makes the preferred core work.

[–] [email protected] 2 points 1 year ago* (last edited 1 year ago) (1 children)

I don't know if we're discussing semantics. A performance score is attributed, and before the fix their scores were all 166. It doesn't work, as you said. So the consequence is the preferred core being "random", isn't it?

[–] [email protected] 1 points 1 year ago

I don't know if it's random, the CPU scheduler still decides what thread to use. It will have its own semantics, but I don't know on what those are based.