Messages in this thread | | | Date | Tue, 21 Jul 2015 19:37:43 +0300 | From | Konstantin Khlebnikov <> | Subject | Re: [PATCH RFC] intel_pstate: play well with frequency limits set by acpi |
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On 21.07.2015 18:37, Srinivas Pandruvada wrote: > On Tue, 2015-07-21 at 13:25 +0300, Konstantin Khlebnikov wrote: >> On 21.07.2015 00:08, Srinivas Pandruvada wrote: >>> On Fri, 2015-07-17 at 07:36 +0300, Konstantin Khlebnikov wrote: >>>> On Fri, Jul 17, 2015 at 1:08 AM, Srinivas Pandruvada >>>> <srinivas.pandruvada@linux.intel.com> wrote: >>>>> On Thu, 2015-07-16 at 21:17 +0300, Konstantin Khlebnikov wrote: >>>>>> IPMI can control CPU P-states remotely: configuration is reported via >>>>>> common ACPI interface (_PPC/_PSS/etc). This patch adds required minimal >>>>>> support in intel_pstate to receive and use these P-state limits. >>>>>> >>>>>> * ignore limit of top state in _PPC: it lower than turbo boost frequency >>>>>> * register intel_pstate in acpi-processor to get states from _PSS >>>>>> * link acpi_processor_get_bios_limit: this adds attribute "bios_limit" >>>>>> >>>>>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> >>>>>> --- >>>>>> drivers/acpi/processor_perflib.c | 3 +- >>>>>> drivers/cpufreq/intel_pstate.c | 57 ++++++++++++++++++++++++++++++++++++++ >>>>>> 2 files changed, 59 insertions(+), 1 deletion(-) >>>>>> >>>>>> diff --git a/drivers/acpi/processor_perflib.c b/drivers/acpi/processor_perflib.c >>>>>> index cfc8aba72f86..781e328c9d5f 100644 >>>>>> --- a/drivers/acpi/processor_perflib.c >>>>>> +++ b/drivers/acpi/processor_perflib.c >>>>>> @@ -98,7 +98,8 @@ static int acpi_processor_ppc_notifier(struct notifier_block *nb, >>>>>> >>>>>> ppc = (unsigned int)pr->performance_platform_limit; >>>>>> >>>>>> - if (ppc >= pr->performance->state_count) >>>>>> + /* Ignore limit of top state: it lower than turbo boost frequency */ >>>>>> + if (!ppc || ppc >= pr->performance->state_count) >>>>> Why? Isn't the previous check enough? >>>> >>>> Zero _PPC state must be top performance state but as I see frequency in >>>> _PSS is lower than maximum possible turbo frequency. So, in this case >>>> intel_pstate cannnot get "100%" for max bound even it there is no limit set. >>>> >>>> For example: I saw _PSS[0] = 2601 Mhz, PSS[1] = 2600 Mhz while turbo >>>> state is 3400 Mhz. >>>> >>> Have you tested dynamic _PPC modification with acpi cpufreq with this >>> change (after boot)? Suppose _PPC is changed from 3 to 0, then >>> cpufreq_verify_within_limits will not be called to change to new max >>> turbo performance state. >>> >> >> I haven't checked that but as I see acpi_processor_ppc_notifier() >> can only reduce maximum frequency. So, there should be no problem >> in this case. > No, it can also be used in both ways. Once reduced, it can increase as > well. _PPC can be dynamically modified by BIOS to reduce and also to > increase.
Well, in this case BIOS will trigger ACPI_PROCESSOR_NOTIFY_PERFORMANCE: kernel evaluate new _PPC and call cpufreq_update_policy() which set initial frequency min/max range according to user setup and apply all limits after that. Initial policy->user_policy.min/max stay unchanged. So, that dynamic modification works in both ways.
-- Konstantin
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