Hi Viresh,

On 04/28/2015 12:18 PM, Viresh Kumar wrote:

On 28 April 2015 at 11:53, Shilpasri G Bhat
[off-list ref] wrote:

quoted

Changes from v1:
- Add macros to define OCC_RESET, OCC_LOAD and OCC_THROTTLE
- Define a structure to store chip id, chip mask which has bits set
  for cpus present in the chip, throttled state and a work_struct.
- Modify powernv_cpufreq_throttle_check() to be called via smp_call()

Why ? I might have missed it but there should be some reasoning behind
what you are changing.

My bad I haven't added explicit comment to state reason behind this change.

I modified the definition of *throttle_check() to match the function definition
to be called via smp_call() instead of adding an additional wrapper around
*throttle_check().

OCC is a chip entity and any local throttle state changes should be associated
to cpus belonging to that chip. The *throttle_check() will read the core
register PMSR to verify throttling. All the cores in a chip will have the same
throttled state as they are managed by a the same OCC in that chip.

smp_call() is required to ensure *throttle_check() is called on a cpu belonging
to the chip for which we have received throttled/unthrottled notification. We
could be handling throttled/unthrottled notification of 'chip1' in 'chip2' so do
an smp_call() on 'chip1'.

We are irq_disabled in powernv_cpufreq_occ_msg() the notification handler.
Thus the use of kworker to do an smp_call and restore policy->cur.

OCC_RESET is global event it affects frequency of all chips. Pmax capping is
local event, it affects the frequency of a chip.

quoted

- On Pmax throttling/unthrottling update 'chip.throttled' and not the
  global 'throttled' as Pmax capping is local to the chip.
- Remove the condition which checks if local pstate is less than Pmin
  while checking for Psafe frequency. When OCC becomes active after
  reset we update 'thottled' to false and when the cpufreq governor
  initiates a pstate change, the local pstate will be in Psafe and we
  will be reporting a false positive when we are not throttled.
- Schedule a kworker on receiving throttling/unthrottling OCC message
  for that chip and schedule on all chips after receiving active.
- After an OCC reset all the cpus will be in Psafe frequency. So call
  target() and restore the frequency to policy->cur after OCC_ACTIVE
  and Pmax unthrottling
- Taken care of Viresh and Preeti's comments.

That's a lot. I am not an expert here and so really can't comment on
the internals of ppc. But, is it patch solving a single problem ? I don't
know, I somehow got the impression that it can be split into multiple
(smaller & review-able) patches. Only if it makes sense. Your call.

All the changes introduced in this patch is centered around opal_message
notification handler powernv_cpufreq_occ_msg(). I can split it into multiple
patches but it all will be relevant only to solve the above problem.

quoted

diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c

quoted

+void powernv_cpufreq_work_fn(struct work_struct *work)
+{
+       struct chip *c = container_of(work, struct chip, throttle);
+       unsigned int cpu;
+
+       smp_call_function_any(&c->mask,
+                             powernv_cpufreq_throttle_check, NULL, 0);
+
+       for_each_cpu(cpu, &c->mask) {

for_each_online_cpu ?

I want to iterate on all the cpus in a chip stored in 'struct chip.mask'.
If you were intending me to avoid 'if(!cpu_online(cpu))' then will the following do:

for_each_cpu_and(cpu, &c->mask, cpu_online_mask)

quoted

+               int index;
+               struct cpufreq_frequency_table *freq_table;
+               struct cpufreq_policy cpu_policy;

Name it policy.

Okay.

quoted

+
+               if (!cpu_online(cpu))
+                       continue;

And you can kill this..

quoted

+               cpufreq_get_policy(&cpu_policy, cpu);
+               freq_table = cpufreq_frequency_get_table(cpu_policy.cpu);

Just do, policy->freq_table.

Okay.

quoted

+static int powernv_cpufreq_occ_msg(struct notifier_block *nb,
+                                  unsigned long msg_type, void *msg)
+{

quoted

+               if (reason && reason <= 5)
+                       pr_info("OCC: Chip %d Pmax reduced due to %s\n",
+                               (int)chip_id, throttle_reason[reason]);
+               else
+                       pr_info("OCC: Chip %d %s\n", (int)chip_id,
+                               throttle_reason[reason]);

Blank line here. They are better for readability after blocks and loops.

Yes will do.

quoted

+               for (i = 0; i < nr_chips; i++)
+                       if (chips[i].id == (int)chip_id)

Why isn't .id 64 bit ?

I guess 6 bits are sufficient to store chip id given that max number of chips
can be 256. I don't have good reason for defining .id 32 bit.

Yeah 64-bit .id will avoid the typecast.

quoted

+                               schedule_work(&chips[i].throttle);
+       }
+       return 0;
+}
+
+static struct notifier_block powernv_cpufreq_opal_nb = {
+       .notifier_call  = powernv_cpufreq_occ_msg,
+       .next           = NULL,
+       .priority       = 0,
+};
+
 static void powernv_cpufreq_stop_cpu(struct cpufreq_policy *policy)
 {
        struct powernv_smp_call_data freq_data;

@@ -414,6 +530,35 @@ static struct cpufreq_driver powernv_cpufreq_driver = {
        .attr           = powernv_cpu_freq_attr,
 };

+static int init_chip_info(void)
+{
+       int chip[256], i = 0, cpu;
+       int prev_chip_id = INT_MAX;
+
+       for_each_possible_cpu(cpu) {
+               int c = cpu_to_chip_id(cpu);

Does 'c' refer to id here ? Name it so then.

Okay.

quoted

+
+               if (prev_chip_id != c) {
+                       prev_chip_id = c;
+                       chip[nr_chips++] = c;
+               }
+       }
+
+       chips = kmalloc_array(nr_chips, sizeof(struct chip), GFP_KERNEL);
+

A blank line isn't preferred much here :). Sorry about these blank lines.

Okay.

Thanks and Regards,
Shilpa