linux-kernel - Re: [PATCH] drm: Do not use BUG_ON(!spin_is

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Date:	Mon, 1 Sep 2014 16:18:35 +1000
From:	Dave Airlie <airlied@...il.com>
To:	sanjeev sharma <sanjeevsharmaengg@...il.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	Rob Clark <robdclark@...il.com>,
	Guenter Roeck <linux@...ck-us.net>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm: Do not use BUG_ON(!spin_is_locked())

>ssert_spin_locked() is a better option.
>> > >
>> >
>> > Unless there's a bug, assert_spin_locked() is just going to incur an
>> > unnecessary cost every time it is called at runtime.  My suggestion was
>> > to
>> > limit that check only to debugging kernels that include enabling lockdep
>> > when tracking down problems rather than needlessly evaluating the
>> > conditional every time when there are no bugs.
>>
>> My experience with gpu drivers (i915) has been that hw and the software
>> running it is varied enough that almost always it's better to
>> unconditionally enable this stuff. I much prefer assert_spin_locked and
>> friends over the lockdep versions since enabling full lockdep is not
>> something you usually do. Especially not normal users, and we rely upon
>> them for testing the old stuff. Furthermore for the modeset code the
>> overhead is totally irrelevant since we're doing metric piles of register
>> reads and writes in there anyway.


Did anything translate into an R-b here?

Dave.
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