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SubjectRe: [PATCH] cpufreq/schedutil: Cleanup and document iowait boost
On 10-04-18, 11:43, Patrick Bellasi wrote:
> On 05-Apr 15:28, Viresh Kumar wrote:
> What about this new version for the two functions,
> just compile tested:
>
> ---8<---
>
> static void sugov_set_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
> unsigned int flags)
> {
> bool iowait = flags & SCHED_CPUFREQ_IOWAIT;
>
> /* Reset boost if the CPU appears to have been idle enough */
> if (sg_cpu->iowait_boost) {
> s64 delta_ns = time - sg_cpu->last_update;
>
> if (delta_ns > TICK_NSEC) {
> sg_cpu->iowait_boost = iowait
> ? sg_cpu->sg_policy->policy->min : 0;

Yeah, I see you are trying to optimize it a bit here but this makes
things more confusing I would say :)

I would just set iowait_boost to 0 and drop the return; from below and
let the code fall through and reach the end of this routine.

> sg_cpu->iowait_boost_pending = iowait;
> return;
> }
> }
>
> /* Boost only tasks waking up after IO */
> if (!iowait)
> return;
>
> /* Ensure IO boost doubles only one time at each frequency increase */
> if (sg_cpu->iowait_boost_pending)
> return;
> sg_cpu->iowait_boost_pending = true;
>
> /* Double the IO boost at each frequency increase */
> if (sg_cpu->iowait_boost) {
> sg_cpu->iowait_boost <<= 1;
> if (sg_cpu->iowait_boost > sg_cpu->iowait_boost_max)
> sg_cpu->iowait_boost = sg_cpu->iowait_boost_max;
> return;
> }
>
> /* At first wakeup after IO, start with minimum boost */
> sg_cpu->iowait_boost = sg_cpu->sg_policy->policy->min;
> }
>
> static void sugov_iowait_boost(struct sugov_cpu *sg_cpu,
> unsigned long *util, unsigned long *max)
> {
> unsigned int boost_util, boost_max;
>
> /* No IOWait boost active */
> if (!sg_cpu->iowait_boost)
> return;
>
> /* An IO waiting task has just woken up, use the boost value */
> if (sg_cpu->iowait_boost_pending) {
> sg_cpu->iowait_boost_pending = false;
> } else {
> /* Reduce the boost value otherwise */
> sg_cpu->iowait_boost >>= 1;
> if (sg_cpu->iowait_boost < sg_cpu->sg_policy->policy->min) {
> sg_cpu->iowait_boost = 0;
> return;
> }
> }
>
> boost_util = sg_cpu->iowait_boost;
> boost_max = sg_cpu->iowait_boost_max;
>
> /*
> * A CPU is boosted only if its current utilization is smaller then
> * the current IO boost level.
> */
> if (*util * boost_max < *max * boost_util) {
> *util = boost_util;
> *max = boost_max;
> }
> }

So this is quite different than what you proposed, it is only fixing
the existing problem which I pointed out to. Looks fine, not much
changed really from the current state of code.

--
viresh

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