[PATCH 3/3] cpufreq: scmi: Register for limit change notifications
Sibi Sankar
quic_sibis at quicinc.com
Tue Jan 16 18:58:36 PST 2024
On 1/10/24 13:56, Lukasz Luba wrote:
> Hi Sibi,
>
Hey Lukasz,
Thanks for taking time to review the series!
> + Morten and Dietmar on CC
>
> On 1/8/24 14:01, Sibi Sankar wrote:
>> Register for limit change notifications if supported with the help of
>> perf_notify_support interface and determine the throttled frequency
>> using the perf_opp_xlate to apply HW pressure.
>>
>> Signed-off-by: Sibi Sankar <quic_sibis at quicinc.com>
>> ---
>> drivers/cpufreq/scmi-cpufreq.c | 42 +++++++++++++++++++++++++++++++++-
>> 1 file changed, 41 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/cpufreq/scmi-cpufreq.c
>> b/drivers/cpufreq/scmi-cpufreq.c
>> index 4ee23f4ebf4a..53bc8868455d 100644
>> --- a/drivers/cpufreq/scmi-cpufreq.c
>> +++ b/drivers/cpufreq/scmi-cpufreq.c
>> @@ -25,9 +25,13 @@ struct scmi_data {
>> int domain_id;
>> int nr_opp;
>> struct device *cpu_dev;
>> + struct cpufreq_policy *policy;
>> cpumask_var_t opp_shared_cpus;
>> + struct notifier_block limit_notify_nb;
>> };
>> +const struct scmi_handle *handle;
>> +static struct scmi_device *scmi_dev;
>> static struct scmi_protocol_handle *ph;
>> static const struct scmi_perf_proto_ops *perf_ops;
>> @@ -144,6 +148,22 @@ scmi_get_cpu_power(struct device *cpu_dev,
>> unsigned long *power,
>> return 0;
>> }
>> +static int scmi_limit_notify_cb(struct notifier_block *nb, unsigned
>> long event, void *data)
>> +{
>> + unsigned long freq_hz;
>> + struct scmi_perf_limits_report *limit_notify = data;
>> + struct scmi_data *priv = container_of(nb, struct scmi_data,
>> limit_notify_nb);
>> + struct cpufreq_policy *policy = priv->policy;
>> +
>> + if (perf_ops->perf_opp_xlate(ph, priv->domain_id,
>> limit_notify->range_max, &freq_hz))
>> + return NOTIFY_OK;
>> +
>> + /* Update HW pressure (the boost frequencies are accepted) */
>> + arch_update_hw_pressure(policy->related_cpus, (freq_hz /
>> HZ_PER_KHZ));
>
> This is wrong. The whole idea of the new HW pressure was that I wanted
> to get rid of the 'signal smoothing' mechanism in order to get
> instantaneous value from FW to task scheduler. Vincent created
> 2 interfaces in that new HW pressure:
> 1. cpufreq_update_pressure(policy) - raw variable
> 2. arch_update_hw_pressure(policy->related_cpus, (freq_hz / HZ_PER_KHZ))
> - smoothing PELT mechanism, good for raw IRQ in drivers
>
> In our SCMI cpufreq driver we need the 1st one:
> cpufreq_update_pressure(policy)
>
> The FW will do the 'signal smoothing or filtering' and won't
> flood the kernel with hundreds of notifications.
Ack, even though I see no mention of filtering being mandated in the
SCMI specification, the scmi notification by itself will serve as a
rate limiter I guess.
>
> So, please change that bit and add me, Morten and Dietmar on CC.
> I would like to review it.
ack
-Sibi
>
> Regards,
> Lukasz
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