Re: [PATCH] staircase scheduler v6.4 for 2.6.7-rc3

[Peter Williams <pwil3058@bigpond.net.au>]

William Lee Irwin III wrote:
> On Wed, Jun 09, 2004 at 09:04:23AM +1000, Peter Williams wrote:
> 
>>There was no need to add the extra overhead of a flag to indicate that a 
>>task was queued for scheduling.  Testing whether run_list is empty 
>>achieves the same thing as reliably as the old array == NULL test did.
> 
> 
> Overhead? Doubtful. Also, that requires the use of list_del_init()

Yes, that's true.

> while dequeueing, which is not in place now. Please do back the claim
> with measurements. It should be easy enough to nop out set_task_queued(),
> implement task_queued() via !list_empty(), and clear_task_queued() via
> INIT_LIST_HEAD() for a quick performance comparison. But I'd say to
> merge it even if there's no difference, as it's more self-contained.
> 

Since the principle use of testing array for NULL or not was to find out 
if the task was on a run list it seems silly to have a flag to determine 
this.  All it does is provide an opportunity for the flag to not 
accurately reflect whether the task is really on a list or not.

It caused the number of files touched by the staircase patch to increase 
  by a factor of five which is another good reason to use the alternative.

Peter
-- 
Dr Peter Williams                                pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce