[EBS-Linux] Re: The semaphore problem w.r.t. "true background" tasks

[John L. <jo...@au...>]

On Fri, 27 Feb 2004, Peter Williams wrote:

> I think that a "flag" based solution to this problem would probably be 
> inadequate as there's no guarantee that a task only holds one semaphore 
> at a time.  So I think that we should investigate a "count" based 
> solution.
 
Wouldn't a better solution to this problem be to ensure that a background 
task running in kernel mode always get a highish priority? It can then 
finish its work in the kernel, be given its background priority back and 
call schedule().

I don't know whether the user_mode() macro could be used within 
sched_normal_effective_prio(), but if it could solving this problem could 
simply be:

static inline int sched_normal_effective_prio(task_t *p, runqueue_t *rq)
{
        uint32_t eps;

        if (unlikely(0 == p->cpu_rate_cap_per_share)) {
                if (user_mode(regs))
                        return EBS_BGND_PRI;
		else
			return EBS_MEAN_PRI;
        }
        ....

Of course 'regs' is undefined above. I'll take a closer look at 
user_mode() and struct pt_regs.

John