Re: [PATCH 3/3] cpufreq: scmi: Register for limit change notifications

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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@xxxxxxxxxxx>
---
  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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