Re: [PATCH] cpuset semaphore depth check optimize

[Andrew Morton]

Paul Jackson <pj@xxxxxxx> wrote:
>
>  +static struct task_struct *cpuset_sem_owner;
>  +static int cpuset_sem_depth;
>   
>   /*
>    * The global cpuset semaphore cpuset_sem can be needed by the
>  @@ -200,16 +202,19 @@ static DECLARE_MUTEX(cpuset_sem);
>   
>   static inline void cpuset_down(struct semaphore *psem)
>   {
>  -	if (current->cpuset_sem_nest_depth == 0)
>  +	if (cpuset_sem_owner != current) {
>   		down(psem);
>  -	current->cpuset_sem_nest_depth++;
>  +		cpuset_sem_owner = current;
>  +	}
>  +	cpuset_sem_depth++;
>   }

Better, but still hacky.  The rest of the kernel manages to avoid the need
for nestable semaphores by getting the locking design sorted out.  Can
cpusets do that sometime?

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