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SubjectRe: [PATCH] sched/fair: util_est: fix cpu_util_wake for execl
On Tue, Oct 30, 2018 at 04:09:47PM +0000, Patrick Bellasi wrote:

> Let's fix this by ensuring to always discount the task estimated
> utilization from the CPU's estimated utilization when the task is also
> the current one. The same benchmark of the bug report, executed on a
> dual socket 40 CPUs Intel(R) Xeon(R) CPU E5-2690 v2 @ 3.00GHz machine,
> reports these "Execl Throughput" figures (higher the better):

Before this we have:

/* Discount task's blocked util from CPU's util */
util -= min_t(unsigned int, util, task_util(p));

at the very least that comment is now inaccurate, since @p might not be
blocked.

> @@ -6258,8 +6267,17 @@ static unsigned long cpu_util_wake(int cpu, struct task_struct *p)
> * covered by the following code when estimated utilization is
> * enabled.
> */
> - if (sched_feat(UTIL_EST))
> - util = max(util, READ_ONCE(cfs_rq->avg.util_est.enqueued));
> + if (sched_feat(UTIL_EST)) {
> + unsigned int estimated =
> + READ_ONCE(cfs_rq->avg.util_est.enqueued);
> +
> + if (unlikely(current == p || task_on_rq_queued(p))) {

I'm confused by the need for 'current == p', afaict task_on_rq_queued(p)
is sufficient -- we've already established task_cpu(p) == cpu earlier.

> + estimated -= min_t(unsigned int, estimated,
> + (_task_util_est(p) | UTIL_AVG_UNCHANGED));
> + }
> +
> + util = max(util, estimated);
> + }

Also, I think it is about time we find a suitable name for:

#define xxx(_var, _val) do { \
typeof(_var) var = (_var); \
typeof(_var) val = (_val); \
typeof(_var) res = var - val; \
if (res > var) \
res = 0; \
(_var) = res; \
} while (0)

Which is basically sub_positive() but without the READ_ONCE/WRITE_ONCE
stuff. We do that:

var -= min_t(typeof(var), var, val);

pattern _all_ over.
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