From: Quentin Perret <quentin.perret@arm.com>
To: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>, Tejun Heo <tj@kernel.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
Paul Turner <pjt@google.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Juri Lelli <juri.lelli@redhat.com>, Todd Kjos <tkjos@google.com>,
Joel Fernandes <joelaf@google.com>,
Steve Muckle <smuckle@google.com>,
Suren Baghdasaryan <surenb@google.com>,
Alessio Balsini <balsini@android.com>
Subject: Re: [PATCH v11 1/5] sched/core: uclamp: Extend CPU's cgroup controller
Date: Mon, 8 Jul 2019 12:08:41 +0100 [thread overview]
Message-ID: <20190708110838.4ohd7pqx5ngkzcsu@queper01-lin> (raw)
In-Reply-To: <20190708084357.12944-2-patrick.bellasi@arm.com>
Hi Patrick,
On Monday 08 Jul 2019 at 09:43:53 (+0100), Patrick Bellasi wrote:
> +static inline int uclamp_scale_from_percent(char *buf, u64 *value)
> +{
> + *value = SCHED_CAPACITY_SCALE;
> +
> + buf = strim(buf);
> + if (strncmp("max", buf, 4)) {
> + s64 percent;
> + int ret;
> +
> + ret = cgroup_parse_float(buf, 2, &percent);
> + if (ret)
> + return ret;
> +
> + percent <<= SCHED_CAPACITY_SHIFT;
> + *value = DIV_ROUND_CLOSEST_ULL(percent, 10000);
> + }
> +
> + return 0;
> +}
> +
> +static inline u64 uclamp_percent_from_scale(u64 value)
> +{
> + return DIV_ROUND_CLOSEST_ULL(value * 10000, SCHED_CAPACITY_SCALE);
> +}
FWIW, I tried the patches and realized these conversions result in a
'funny' behaviour from a user's perspective. Things like this happen:
$ echo 20 > cpu.uclamp.min
$ cat cpu.uclamp.min
20.2
$ echo 20.2 > cpu.uclamp.min
$ cat cpu.uclamp.min
20.21
Having looked at the code, I get why this is happening, but I'm not sure
if a random user will. It's not an issue per se, but it's just a bit
weird.
I guess one way to fix this would be to revert back to having a
1024-scale for the cgroup interface too ... Though I understand Tejun
wanted % for consistency with other things.
So, I'm not sure if this is still up for discussion, but in any case I
wanted to say I support your original idea of using a 1024-scale for the
cgroups interface, since that would solve the 'issue' above and keeps
things consistent with the per-task API too.
Thanks,
Quentin
next prev parent reply other threads:[~2019-07-08 11:08 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-08 8:43 [PATCH v11 0/5] Add utilization clamping support (CGroups API) Patrick Bellasi
2019-07-08 8:43 ` [PATCH v11 1/5] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
2019-07-08 11:08 ` Quentin Perret [this message]
2019-07-15 13:38 ` Patrick Bellasi
2019-07-18 14:52 ` Tejun Heo
2019-07-18 15:26 ` Patrick Bellasi
2019-07-08 8:43 ` [PATCH v11 2/5] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
2019-07-15 16:42 ` Michal Koutný
2019-07-16 14:07 ` Patrick Bellasi
2019-07-16 15:29 ` Michal Koutný
2019-07-16 17:55 ` Patrick Bellasi
2019-07-08 8:43 ` [PATCH v11 3/5] sched/core: uclamp: Propagate system defaults to root group Patrick Bellasi
2019-07-15 16:42 ` Michal Koutný
2019-07-16 14:34 ` Patrick Bellasi
2019-07-16 15:36 ` Michal Koutný
2019-07-16 18:00 ` Patrick Bellasi
2019-07-16 15:46 ` Joel Fernandes
2019-07-08 8:43 ` [PATCH v11 4/5] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps Patrick Bellasi
2019-07-15 16:42 ` Michal Koutný
2019-07-16 14:34 ` Patrick Bellasi
2019-07-16 15:58 ` Michal Koutný
2019-07-08 8:43 ` [PATCH v11 5/5] sched/core: uclamp: Update CPU's refcount on TG's clamp changes Patrick Bellasi
2019-07-15 16:51 ` [PATCH v11 0/5] Add utilization clamping support (CGroups API) Michal Koutný
2019-07-16 14:03 ` Patrick Bellasi
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