From: Valentin Schneider <valentin.schneider@arm.com>
To: Qais Yousef <qais.yousef@arm.com>
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
mingo@kernel.org, vincent.guittot@linaro.org,
dietmar.eggemann@arm.com, patrick.bellasi@matbug.net,
qperret@google.com, morten.rasmussen@arm.com
Subject: Re: [PATCH 3/3] sched/fair: Consider uclamp for "task fits capacity" checks
Date: Mon, 25 Nov 2019 17:33:21 +0000 [thread overview]
Message-ID: <c76d2b10-c4a8-465e-9310-030efe75a64e@arm.com> (raw)
In-Reply-To: <20191124222051.kbb62phfsln5ixg4@e107158-lin.cambridge.arm.com>
On 24/11/2019 22:20, Qais Yousef wrote:
> On 11/20/19 17:55, Valentin Schneider wrote:
>> +static inline
>> +unsigned long uclamp_task_util(struct task_struct *p, unsigned long util)
>> +{
>> + return clamp(util,
>> + (unsigned long)uclamp_eff_value(p, UCLAMP_MIN),
>> + (unsigned long)uclamp_eff_value(p, UCLAMP_MAX));
>> +}
>
> uclamp_eff_value() will check if a task belongs to a cgroup, and if it does
> apply its uclamp. The funny thing about the cgroup settings is that they can
> have a uclamp_max < uclamp_min. uclamp_util_with() does check for this
> condition but this function doesn't.
>
So according to comments, uclamp_util_with() has to check for inversion
because it is comparing task clamps with rq-wide aggregated clamps.
However I have to admit I still am not clear as to how a clamp inversion
can occur. Without cgroups, it all goes through
__sched_setscheduler() -> uclamp_validate()
which enforces uclamp.min <= uclamp.max. So the rq-wide aggregation could
not lead to an inversion.
With cgroups, I do recall something about allowing the cgroup *knobs* to be
inverted, but AFAICT that gets sanitized when it trickles down to the
scheduler via cpu_util_update_eff():
eff[UCLAMP_MIN] = min(eff[UCLAMP_MIN], eff[UCLAMP_MAX]);
So I don't see how inversion could happen within uclamp_task_util().
Patrick, any chance you could light up my torch?
FWIW I gave this a spin but couldn't create an inversion inside the
scheduler (debug prints appended at the end):
$ cgcreate -g cpu:cgtest
$ ./loop.sh &
$ PID=$!
$ echo $PID > /sys/fs/cgroup/cpu/cgtest/cgroup.procs
$ echo 20 > /sys/fs/cgroup/cpu/cgtest/cpu.uclamp.max
[ 24.442204] tg=00000000b546653d clamp_id=1 value=205
[ 24.447169] css=00000000b546653d uclamp.min=0 uclamp.max=205
[ 24.452932] p=loop.sh tg.uclamp.min=0 tg.uclamp.max=205 p.uclamp.min=0 p.uclamp.max=1024
[ 24.461021] p=loop.sh uclamp.min=0 uclamp.max=205
$ echo 80 > /sys/fs/cgroup/cpu/cgtest/cpu.uclamp.min
[ 25.472174] tg=00000000b546653d clamp_id=0 value=819
[ 25.477135] css=00000000b546653d uclamp.min=205 uclamp.max=205
[ 25.483066] p=loop.sh tg.uclamp.min=205 tg.uclamp.max=205 p.uclamp.min=0 p.uclamp.max=1024
[ 25.491311] p=loop.sh uclamp.min=205 uclamp.max=205
---
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2da6a005bb3f..7b31fdc7cc90 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1088,6 +1088,17 @@ uclamp_update_active_tasks(struct cgroup_subsys_state *css,
if ((0x1 << clamp_id) & clamps)
uclamp_update_active(p, clamp_id);
}
+ pr_info("p=%s tg.uclamp.min=%u tg.uclamp.max=%u "
+ "p.uclamp.min=%u p.uclamp.max=%u\n",
+ p->comm, task_group(p)->uclamp[UCLAMP_MIN].value,
+ task_group(p)->uclamp[UCLAMP_MAX].value,
+ p->uclamp_req[UCLAMP_MIN].value,
+ p->uclamp_req[UCLAMP_MAX].value);
+
+
+ pr_info("p=%s uclamp.min=%u uclamp.max=%u\n",
+ p->comm, uclamp_tg_restrict(p, UCLAMP_MIN).value,
+ uclamp_tg_restrict(p, UCLAMP_MAX).value);
}
css_task_iter_end(&it);
}
@@ -7195,6 +7206,8 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css)
/* Ensure protection is always capped by limit */
eff[UCLAMP_MIN] = min(eff[UCLAMP_MIN], eff[UCLAMP_MAX]);
+ pr_info("css=%p uclamp.min=%i uclamp.max=%i\n", css, eff[UCLAMP_MIN], eff[UCLAMP_MAX]);
+
/* Propagate most restrictive effective clamps */
clamps = 0x0;
uc_se = css_tg(css)->uclamp;
@@ -7273,8 +7286,10 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
rcu_read_lock();
tg = css_tg(of_css(of));
- if (tg->uclamp_req[clamp_id].value != req.util)
+ if (tg->uclamp_req[clamp_id].value != req.util) {
+ pr_info("tg=%p clamp_id=%i value=%llu\n", tg, clamp_id, req.util);
uclamp_se_set(&tg->uclamp_req[clamp_id], req.util, false);
+ }
/*
* Because of not recoverable conversion rounding we keep track of the
next prev parent reply other threads:[~2019-11-25 17:33 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-20 17:55 [PATCH 0/3] sched/fair: Task placement biasing using uclamp Valentin Schneider
2019-11-20 17:55 ` [PATCH 1/3] sched/uclamp: Make uclamp_util_*() helpers use and return UL values Valentin Schneider
2019-11-20 17:55 ` [PATCH 2/3] sched/uclamp: Rename uclamp_util_*() into uclamp_rq_util_*() Valentin Schneider
2019-11-20 17:55 ` [PATCH 3/3] sched/fair: Consider uclamp for "task fits capacity" checks Valentin Schneider
2019-11-21 11:56 ` Quentin Perret
2019-11-21 12:56 ` Valentin Schneider
2019-11-21 13:30 ` Quentin Perret
2019-11-21 14:51 ` Valentin Schneider
2019-11-21 15:30 ` Quentin Perret
2019-11-21 17:22 ` Valentin Schneider
2019-11-24 22:20 ` Qais Yousef
2019-11-25 17:33 ` Valentin Schneider [this message]
2019-11-26 10:06 ` Qais Yousef
2019-11-21 12:00 ` [PATCH 0/3] sched/fair: Task placement biasing using uclamp Quentin Perret
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