Commit 4d81b0f9 authored Jul 18, 2018 by Rafael J. Wysocki

cpufreq: pcc-cpufreq: Disable dynamic scaling on many-CPU systems



The firmware interface used by the pcc-cpufreq driver is
fundamentally not scalable and using it for dynamic CPU performance
scaling on systems with many CPUs leads to degraded performance.

For this reason, disable dynamic CPU performance scaling on systems
with pcc-cpufreq where the number of CPUs present at the driver init
time is greater than 4.  Also make the driver print corresponding
complaints to the kernel log.

Reported-by: Andreas Herrmann <aherrmann@suse.com>
Tested-by: Andreas Herrmann <aherrmann@suse.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

parent f54ab690

drivers/cpufreq/pcc-cpufreq.c

+9 −0

Original line number	Original line	Diff line number	Diff line
	@@ -589,6 +589,15 @@ static int __init pcc_cpufreq_init(void)
	return ret;		return ret;
	}		}

			if (num_present_cpus() > 4) {
			pcc_cpufreq_driver.flags \|= CPUFREQ_NO_AUTO_DYNAMIC_SWITCHING;
			pr_err("%s: Too many CPUs, dynamic performance scaling disabled\n",
			__func__);
			pr_err("%s: Try to enable another scaling driver through BIOS settings\n",
			__func__);
			pr_err("%s: and complain to the system vendor\n", __func__);
			}

	ret = cpufreq_register_driver(&pcc_cpufreq_driver);		ret = cpufreq_register_driver(&pcc_cpufreq_driver);

	return ret;		return ret;

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