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SubjectRe: [PATCH 08/10] posix-cpu-timers: Migrate to use new tick dependency mask model
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On 07/23/2015 12:42 PM, Frederic Weisbecker wrote:
> +static void cpu_timer_list_dequeue(struct cpu_timer_list *t)
> +{
> + if (!list_empty(&t->entry))
> + cpu_timer_dec_tick_dependency();
> + list_del_init(&t->entry);
> +}

Is the list_empty() test necessary? It wasn't in the original
posix-timers code, and it feels like a pretty serious bug if you're
doing a list_del on an empty list.

At a higher level, is the posix-cpu-timers code here really providing
the right semantics? It seems like before, the code was checking a
struct task-specific state, and now you are setting a global state such
that if ANY task anywhere in the system (even on housekeeping cores) has
a pending posix cpu timer, then nothing can go into nohz_full mode.

Perhaps what is needed is a task_struct->tick_dependency to go along
with the system-wide and per-cpu flag words?
--
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com


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