Messages in this thread | | | Date | Wed, 21 Dec 2011 19:31:59 +0100 | From | Manfred Spraul <> | Subject | Re: Subject: [PATCH 2/2] priority System V Semaphores |
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Hi raz,
On 12/20/2011 11:23 PM, raz ben yehuda wrote: > > From 25aa166505aff2561dd715c927c654d0bbb432ba Mon Sep 17 00:00:00 2001 > From: raz<raziebe@gmail.com> > Date: Tue, 20 Dec 2011 22:54:56 +0200 > > > Add positioning routine find_pos. find_pos returns > the place where to put the sleeper before. > I sort only rt tasks, OTHER policy is pushed back in > queue. I do not distinct between SCHED_RR and SCHED_FIFO > policies and they are treated as a single policy > for the sorting algorithm. > > SETPRIO operates only when user issues a single semop > operation and not an array of opretions. As far as I can see, the advantages of sysvsem are backward compatibility and the ability to use complex ops. You propose to add a new feature that doesn't work on complex ops.
Are there any apps that use SETPRIO? What is the use case? > SETFIFO is the default for backward compatbility. > > Signed-off-by: raz<raziebe@gmail.com> > --- > ipc/sem.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++-- > 1 files changed, 49 insertions(+), 2 deletions(-) > > diff --git a/ipc/sem.c b/ipc/sem.c > index 90dc5a1..921056d 100644 > --- a/ipc/sem.c > +++ b/ipc/sem.c > @@ -1343,6 +1343,51 @@ static int get_queue_result(struct sem_queue *q) > return error; > } > > +/* > + * find the best place to put the task sorted by rt prio > +*/ > +static struct list_head *find_pos(struct sem *curr, int alter, > + struct task_struct *p) > +{ > + struct sem_queue *q; > + struct sem_queue *ret_pos = NULL; > + struct list_head *tasks_queue =&curr->sem_pending; > + > + if (!alter) > + return tasks_queue; > + Tasks that do not alter anything end up first - IMHO correct.
> + if (!(curr->flags& PRIO_SEM)) > + return tasks_queue; > + /* > + * make no effort to sort SCHED_OTHER, > + * just push task to the back of the queue. > + */ > + if (!(p->policy == SCHED_FIFO || p->policy == SCHED_RR)) > + return tasks_queue; > + /* > + * make no distinction between SCHED_FIFO > + * and SCHED_RR policies. > + */ > + list_for_each_entry(q, tasks_queue, simple_list) { > + struct task_struct *t; > + > + t = q->sleeper; > + if (current->rt_priority == t->rt_priority) { > + /* > + * push in a FIFO manner > + * tasks in same priority > + */ > + ret_pos = q; > + continue; > + } > + if (current->rt_priority< t->rt_priority) > + continue; > + return&q->simple_list; > + } Here in the loop, non-alter tasks are evaluated as well. I think that's wrong, it could starve non-alter tasks.
e.g. queue: - high prio non-alter - low prio non-alter.
Now a medium prio alter task is added. I think it will end up in the wrong position (before the low-prio non-alter task), correct?
-- Manfred
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