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Message-ID: <553F426B.3050601@linux.vnet.ibm.com>
Date: Tue, 28 Apr 2015 13:48:51 +0530
From: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
To: Viresh Kumar <viresh.kumar@...aro.org>
CC: "linuxppc-dev@...abs.org" <linuxppc-dev@...abs.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] cpufreq: powernv: Register for OCC related opal_message
notification
Hi Viresh,
On 04/28/2015 12:18 PM, Viresh Kumar wrote:
> On 28 April 2015 at 11:53, Shilpasri G Bhat
> <shilpa.bhat@...ux.vnet.ibm.com> wrote:
>
>> 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.
>
>> - 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.
>
>> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
>
>> +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)
>
>> + int index;
>> + struct cpufreq_frequency_table *freq_table;
>> + struct cpufreq_policy cpu_policy;
>
> Name it policy.
Okay.
>
>> +
>> + if (!cpu_online(cpu))
>> + continue;
>
> And you can kill this..
>
>> + cpufreq_get_policy(&cpu_policy, cpu);
>> + freq_table = cpufreq_frequency_get_table(cpu_policy.cpu);
>
> Just do, policy->freq_table.
Okay.
>
>
>> +static int powernv_cpufreq_occ_msg(struct notifier_block *nb,
>> + unsigned long msg_type, void *msg)
>> +{
>
>> + 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.
>
>> + 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.
>
>> + 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.
>
>> +
>> + 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
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