lkml.org 
[lkml]   [2009]   [Jan]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] psmouse: run kpsmoused only while needed
On Mon, Jan 26, 2009 at 02:32:10PM -0800, Andrew Morton wrote:
> On Thu, 15 Jan 2009 16:16:19 -0800 (PST)
> Frederic Weisbecker <fweisbec@gmail.com> wrote:
>
> > While looking at the workqueue tracer, I noticed that kpsmoused receives
> > rarely (if not never) events.
> >
> > Currently, when a mouse has to resync, it uses the kpsmoused singlethreaded
> > workqueue. But recync are rare. While reading an old discussion, it seems
> > that usual workqueue events can't be used for that purpose because resync
> > can take too much time and could delay the other works in queue.
> >
> > But if you have built psmouse driver, this workqueue will always be present
> > whether you have a ps/2 port or not. And its events are rare.
> >
> > To avoid this pointless task, this patch makes the kpsmoused a kernel
> > thread only created on the fly when a recync is needed. Once the recync is done,
> > this thread will die. So you will almost never see it, and it will not be
> > an inactive task anymore.
> >
> > This thread is created through a usual workqueue event (because we can't create
> > it from interrupt).
> >
>
> Seems like a reasonable objective.
>
> >
> > ...
> >
> > /*
> > * __psmouse_set_state() sets new psmouse state and resets all flags.
> > @@ -313,7 +307,8 @@ static irqreturn_t psmouse_interrupt(struct serio *serio,
> > psmouse->name, psmouse->phys, psmouse->pktcnt);
> > psmouse->badbyte = psmouse->packet[0];
> > __psmouse_set_state(psmouse, PSMOUSE_RESYNCING);
> > - psmouse_queue_work(psmouse, &psmouse->resync_work, 0);
> > + atomic_inc(&psmouse->nb_recync_pending);
>
> The patch and the changelog consistently misspell "sync".
>
> A code comment (in psmouse.h) which clearly spells out the role of
> nb_recync_pending would be useful.


Ok.


> > + schedule_work(&psmouse->resync_work);
> > goto out;
> > }
> >
> >
> > ...
> >
> > @@ -1131,7 +1155,13 @@ static void psmouse_disconnect(struct serio *serio)
> >
> > /* make sure we don't have a resync in progress */
> > mutex_unlock(&psmouse_mutex);
> > - flush_workqueue(kpsmoused_wq);
> > +
> > + prepare_to_wait(&psmouse->recync_pending_queue, &wait,
> > + TASK_UNINTERRUPTIBLE);
> > + if (atomic_read(&psmouse->nb_recync_pending))
> > + schedule();
> > + finish_wait(&psmouse->recync_pending_queue, &wait);
>
> So... we're requiring that nb_recync_pending is zero at this stage?
>
> I wonder if the code manages to do that. A little WARN_ON(), maybe?


Yes it is supposed to be zero since no new recync can be performed at this time.
But a workqueue (one that creates the kpsmoused thread) or the thread itself can
be still running, so we want to ensure all is completed.

Perhaps a schedule_timeout with a warn_on would be better to detect soft-lockups?

Thanks!


> > mutex_lock(&psmouse_mutex);
> >
>



\
 
 \ /
  Last update: 2009-01-27 01:37    [W:0.598 / U:0.096 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site