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Message-ID: <20181107131632.GP9781@hirez.programming.kicks-ass.net>
Date: Wed, 7 Nov 2018 14:16:32 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Patrick Bellasi <patrick.bellasi@....com>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
Paul Turner <pjt@...gle.com>,
Quentin Perret <quentin.perret@....com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Morten Rasmussen <morten.rasmussen@....com>,
Juri Lelli <juri.lelli@...hat.com>,
Todd Kjos <tkjos@...gle.com>,
Joel Fernandes <joelaf@...gle.com>,
Steve Muckle <smuckle@...gle.com>,
Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v5 03/15] sched/core: uclamp: map TASK's clamp values
into CPU's clamp groups
On Mon, Oct 29, 2018 at 06:32:57PM +0000, Patrick Bellasi wrote:
> +static void uclamp_group_put(unsigned int clamp_id, unsigned int group_id)
> {
> + union uclamp_map *uc_maps = &uclamp_maps[clamp_id][0];
> + union uclamp_map uc_map_old, uc_map_new;
> + long res;
> +
> +retry:
> +
> + uc_map_old.data = atomic_long_read(&uc_maps[group_id].adata);
> + uc_map_new = uc_map_old;
> + uc_map_new.se_count -= 1;
> + res = atomic_long_cmpxchg(&uc_maps[group_id].adata,
> + uc_map_old.data, uc_map_new.data);
> + if (res != uc_map_old.data)
> + goto retry;
> +}
Please write cmpxchg loops in the form:
atomic_long_t *ptr = &uclamp_maps[clamp_id][group_id].adata;
union uclamp_map old, new;
old.data = atomic_long_read(ptr);
do {
new.data = old.data;
new.se_cound--;
} while (!atomic_long_try_cmpxchg(ptr, &old.data, new.data));
(same for all the others of course)
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