linux-kernel - Re: [RFC PATCH 4/6] Make DRM use the tasklet is-sched API

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Message-ID: <20070622182411.GA17658@infradead.org>
Date:	Fri, 22 Jun 2007 19:24:11 +0100
From:	Christoph Hellwig <hch@...radead.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Walker <dwalker@...sta.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	john stultz <johnstul@...ibm.com>,
	Oleg Nesterov <oleg@...sign.ru>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>, matthew.wilcox@...com,
	kuznet@....inr.ac.ru
Subject: Re: [RFC PATCH 4/6] Make DRM use the tasklet is-sched API

On Fri, Jun 22, 2007 at 06:10:55PM +0200, Arnd Bergmann wrote:
> On Friday 22 June 2007, Thomas Gleixner wrote:
> > > > Index: linux-2.6.21-rt9/drivers/char/drm/drm_irq.c
> > > > ===================================================================
> > > > --- linux-2.6.21-rt9.orig/drivers/char/drm/drm_irq.c
> > > > +++ linux-2.6.21-rt9/drivers/char/drm/drm_irq.c
> > > > @@ -461,7 +461,7 @@ void drm_locked_tasklet(drm_device_t *de
> > > > ????static DECLARE_TASKLET(drm_tasklet, drm_locked_tasklet_func, 0);
> > > > ?
> > > > ????if (!drm_core_check_feature(dev, DRIVER_HAVE_IRQ) ||
> > > > -??? ? ?test_bit(TASKLET_STATE_SCHED, &drm_tasklet.state))
> > > > +??? ? ?tasklet_is_scheduled(&drm_tasklet))
> > > > ????????????return;
> > > > ?
> > > > ????spin_lock_irqsave(&dev->tasklet_lock, irqflags);
> > > > 
> > > 
> > > 
> > > No sense in having a patch just for this, may as well merge this with
> > > patch 3 ..
> > 
> > Wrong. patch 3 adds the API and this one makes use of it. Stevens split
> > makes perfectly sense.
> 
> Wouldn't the easy solution be to get rid of drm_locked_tasklet
> entirely and convert i915_vblank_tasklet(), the only user, to use
> a work queue right away?
> 
> The drm_locked_tasklet() function seems to have multiple bugs anyway,
> so getting rid of it can only help, and it avoids exporting a new
> tasklet_is_scheduled() interface.

That's exactly what I though when looking over this code.  There's
some really crappy in code in that area, and it should simply be
rewritten.
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