On 05/19/2017 09:10 AM, Joel Fernandes wrote:
> Hi Viresh,
>
> On Thu, May 18, 2017 at 11:50 PM, Viresh Kumar <[email protected]> wrote:
>> On 18-05-17, 23:23, Joel Fernandes wrote:
>>> We should apply the iowait boost only if cpufreq policy has iowait boost
>>> enabled. Also make it a schedutil configuration from sysfs so it can be turned
>>> on/off if needed (by default initialize it to the policy value).
>>>
>>> For systems that don't need/want it enabled, such as those on arm64 based
>>> mobile devices that are battery operated, it saves energy when the cpufreq
>>> driver policy doesn't have it enabled (details below):
>>>
>>> Here are some results for energy measurements collected running a YouTube video
>>> for 30 seconds:
>>> Before: 8.042533 mWh
>>> After: 7.948377 mWh
>>> Energy savings is ~1.2%
>>>
>>> Cc: Srinivas Pandruvada <[email protected]>
>>> Cc: Len Brown <[email protected]>
>>> Cc: Rafael J. Wysocki <[email protected]>
>>> Cc: Viresh Kumar <[email protected]>
>>> Cc: Ingo Molnar <[email protected]>
>>> Cc: Peter Zijlstra <[email protected]>
>>> Signed-off-by: Joel Fernandes <[email protected]>
>>> ---
>>> kernel/sched/cpufreq_schedutil.c | 32 ++++++++++++++++++++++++++++++++
>>> 1 file changed, 32 insertions(+)
>>>
>>> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
>>> index 76877a62b5fa..0e392b58b9b3 100644
>>> --- a/kernel/sched/cpufreq_schedutil.c
>>> +++ b/kernel/sched/cpufreq_schedutil.c
>>> @@ -24,6 +24,7 @@
>>> struct sugov_tunables {
>>> struct gov_attr_set attr_set;
>>> unsigned int rate_limit_us;
>>> + bool iowait_boost_enable;
>>
>> I suggested s/iowait_boost_enable/iowait_boost/ and you said okay for
>> that change.
>
> Yes, I somehow only picked up 'bool' from your comment. I'll drop the
> '_enable' in the next version. Sorry and thanks.
>
>>> };
>>>
>>> struct sugov_policy {
>>> @@ -171,6 +172,11 @@ static void sugov_get_util(unsigned long *util, unsigned long *max)
>>> static void sugov_set_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
>>> unsigned int flags)
>>> {
>>> + struct sugov_policy *sg_policy = sg_cpu->sg_policy;
>>> +
>>> + if (!sg_policy->tunables->iowait_boost_enable)
>>> + return;
>>> +
>>> if (flags & SCHED_CPUFREQ_IOWAIT) {
>>> sg_cpu->iowait_boost = sg_cpu->iowait_boost_max;
>>> } else if (sg_cpu->iowait_boost) {
>>> @@ -386,10 +392,34 @@ static ssize_t rate_limit_us_store(struct gov_attr_set *attr_set, const char *bu
>>> return count;
>>> }
>>>
>>> +static ssize_t iowait_boost_enable_show(struct gov_attr_set *attr_set,
>>> + char *buf)
>>> +{
>>> + struct sugov_tunables *tunables = to_sugov_tunables(attr_set);
>>> +
>>> + return sprintf(buf, "%u\n", tunables->iowait_boost_enable);
>>> +}
>>> +
>>> +static ssize_t iowait_boost_enable_store(struct gov_attr_set *attr_set,
>>> + const char *buf, size_t count)
>>> +{
>>> + struct sugov_tunables *tunables = to_sugov_tunables(attr_set);
>>> + bool enable;
>>> +
>>> + if (kstrtobool(buf, &enable))
>>> + return -EINVAL;
>>> +
>>> + tunables->iowait_boost_enable = enable;
>>> +
>>> + return count;
>>> +}
>>> +
>>> static struct governor_attr rate_limit_us = __ATTR_RW(rate_limit_us);
>>> +static struct governor_attr iowait_boost_enable = __ATTR_RW(iowait_boost_enable);
>>>
>>> static struct attribute *sugov_attributes[] = {
>>> &rate_limit_us.attr,
>>> + &iowait_boost_enable.attr,
>>> NULL
>>> };
>>
>> Do we really need this right now? I mean, are you going to use it this
>> way? It may never get used eventually and may be better to leave the
>> sysfs option for now.
>
> I felt it is good to leave it to the system designer and have the
> policy set a 'default' value, so incase it isn't touched by the
> designer from userspace, then the policy default is fine, and if the
> designer chooses to change it then he has the option to. This is also
> how we currently set the rate limits for schedutil in android. I don't
> feel strongly about one way or the other and if the general consensus
> is to drop this part then I'm fine. I'm curious to know what others
> think as well though.
>
Acked-by: Saravana Kannan <[email protected]>
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