From: Rafael J. Wysocki <[email protected]> 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 <[email protected]> Signed-off-by: Rafael J. Wysocki <[email protected]> --- drivers/cpufreq/pcc-cpufreq.c | 8 ++++++++ 1 file changed, 8 insertions(+) Index: linux-pm/drivers/cpufreq/pcc-cpufreq.c =================================================================== --- linux-pm.orig/drivers/cpufreq/pcc-cpufreq.c +++ linux-pm/drivers/cpufreq/pcc-cpufreq.c @@ -589,6 +589,14 @@ static int __init pcc_cpufreq_init(void) return ret; } + if (num_present_cpus() > 4) { + pcc_cpufreq_driver.flags |= CPUFREQ_NO_AUTO_DYNAMIC_SWITCHING; + pr_err("%s: Unsuitable system, dynamic performance scaling disabled\n", + __func__); + pr_err("%s: Change BIOS settings and complain to the hardware vendor\n", + __func__); + } + ret = cpufreq_register_driver(&pcc_cpufreq_driver); return ret;
