6.6-stable review patch. If anyone has any objections, please let me know.
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From: Rafael J. Wysocki rafael.j.wysocki@intel.com
commit a1ff59784b277795a613beaa5d3dd9c5595c69a7 upstream.
It is reported that single-thread performance on some hybrid systems dropped significantly after commit 7feec7430edd ("ACPI: CPPC: Only probe for _CPC if CPPC v2 is acked") which prevented _CPC from being used if the support for it had not been confirmed by the platform firmware.
The problem is that if the platform firmware does not confirm CPPC v2 support, cppc_get_perf_caps() returns an error which prevents the intel_pstate driver from enabling ITMT. Consequently, the scheduler does not get any hints on CPU performance differences, so in a hybrid system some tasks may run on CPUs with lower capacity even though they should be running on high-capacity CPUs.
To address this, modify intel_pstate to use the information from MSR_HWP_CAPABILITIES to enable ITMT if CPPC is not available (which is done already if the highest performance number coming from CPPC is not realistic).
Fixes: 7feec7430edd ("ACPI: CPPC: Only probe for _CPC if CPPC v2 is acked") Closes: https://lore.kernel.org/linux-acpi/d01b0a1f-bd33-47fe-ab41-43843d8a374f@kfoc... Link: https://lore.kernel.org/linux-acpi/ZnD22b3Br1ng7alf@kf-XE Reported-by: Aaron Rainbolt arainbolt@kfocus.org Tested-by: Aaron Rainbolt arainbolt@kfocus.org Cc: 5.19+ stable@vger.kernel.org # 5.19+ Link: https://patch.msgid.link/12460110.O9o76ZdvQC@rjwysocki.net Signed-off-by: Rafael J. Wysocki rafael.j.wysocki@intel.com Reviewed-by: Mario Limonciello mario.limonciello@amd.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/cpufreq/intel_pstate.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-)
--- a/drivers/cpufreq/intel_pstate.c +++ b/drivers/cpufreq/intel_pstate.c @@ -356,15 +356,14 @@ static void intel_pstate_set_itmt_prio(i int ret;
ret = cppc_get_perf_caps(cpu, &cppc_perf); - if (ret) - return; - /* - * On some systems with overclocking enabled, CPPC.highest_perf is hardcoded to 0xff. - * In this case we can't use CPPC.highest_perf to enable ITMT. - * In this case we can look at MSR_HWP_CAPABILITIES bits [8:0] to decide. + * If CPPC is not available, fall back to MSR_HWP_CAPABILITIES bits [8:0]. + * + * Also, on some systems with overclocking enabled, CPPC.highest_perf is + * hardcoded to 0xff, so CPPC.highest_perf cannot be used to enable ITMT. + * Fall back to MSR_HWP_CAPABILITIES then too. */ - if (cppc_perf.highest_perf == CPPC_MAX_PERF) + if (ret || cppc_perf.highest_perf == CPPC_MAX_PERF) cppc_perf.highest_perf = HWP_HIGHEST_PERF(READ_ONCE(all_cpu_data[cpu]->hwp_cap_cached));
/*