linux-kernel - Re: [RFC][PATCH] ipc: mqueue: wq_add priority changed to dynamic priority

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Date:   Mon, 11 Dec 2017 19:54:33 +0000
From:   Jonathan Haws <jhaws@....usu.edu>
To:     "rostedt@...dmis.org" <rostedt@...dmis.org>
CC:     "bigeasy@...utronix.de" <bigeasy@...utronix.de>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "deepa.kernel@...il.com" <deepa.kernel@...il.com>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
        "arnd@...db.de" <arnd@...db.de>
Subject: Re: [RFC][PATCH] ipc: mqueue: wq_add priority changed to dynamic
 priority

On Mon, 2017-12-11 at 14:32 -0500, Steven Rostedt wrote:
> On Mon, 11 Dec 2017 17:12:05 +0000
> Jonathan Haws <jhaws@....usu.edu> wrote:
> 
> > 
> > Adding linux-rt-users group to thread.
> > ________________________________________
> > From: Jonathan Haws <jhaws@....usu.edu>
> > Sent: Monday, December 11, 2017 08:37
> > To: mingo@...nel.org; viro@...iv.linux.org.uk; arnd@...db.de; akpm@
> > linux-foundation.org; deepa.kernel@...il.com
> > Cc: linux-kernel@...r.kernel.org; tglx@...utronix.de; bigeasy@...ut
> > ronix.de; rostedt@...dmis.org; Jonathan Haws
> > Subject: [RFC][PATCH] ipc: mqueue: wq_add priority changed to
> > dynamic priority
> > 
> > Previous behavior added tasks to the work queue using the
> > static_prio value
> > instead of the dynamic priority value in prio. This caused RT tasks
> > to be
> > added to the work queue in a FIFO manner rather than by priority.
> > Normal
> > tasks were handled by priority.
> > 
> > This fix utilizes the dynamic priority of the task to ensure that
> > both RT
> > and normal tasks are added to the work queue in priority order.
> > Utilizing
> > the dynamic priority (prio) rather than the base priority
> > (normal_prio) was
> > chosen to ensure that if a task had a boosted priority when it was
> > added to
> > the work queue, it would be woken sooner to to ensure that it
> > releases any
> > other locks it may be holding in a more timely manner. It is
> > understood that
> > the task could have a lower priority when it wakes than when it was
> > added to
> > the queue in this (unlikely) case.
> Probably a better subject would be:
> 
>  ipc: mqueue: Have RT tasks queue in by priority in wq_add()

Is the best way to change that just to change it in the email thread or
resubmit the patch as v2?

> 
> Other than that (and that this doesn't handle DL tasks),
> 
> Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> 
> -- Steve
> 

I'm still new to kernel scheduling details - can you elaborate on what
a DL task is?  I'm happy to update the patch to handle DL tasks as well
if it makes sense to do so.

Thanks!
Jon

> > 
> > 
> > Signed-off-by: Jonathan Haws <jhaws@....usu.edu>
> > ---
> >  ipc/mqueue.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/ipc/mqueue.c b/ipc/mqueue.c
> > index 9649ecd..cb96db9 100644
> > --- a/ipc/mqueue.c
> > +++ b/ipc/mqueue.c
> > @@ -546,7 +546,7 @@ static void wq_add(struct mqueue_inode_info
> > *info, int sr,
> >         ewp->task = current;
> > 
> >         list_for_each_entry(walk, &info->e_wait_q[sr].list, list) {
> > -               if (walk->task->static_prio <= current-
> > >static_prio) {
> > +               if (walk->task->prio <= current->prio) {
> >                         list_add_tail(&ewp->list, &walk->list);
> >                         return;
> >                 }
> > --
> > 2.7.4
> >