Re: [PATCH] cpuset semaphore depth check optimize

Andrew Morton
2005-09-12T11:41:44Z

Paul Jackson <pj@sgi.com> 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?