yes you are absolutely correct and the change I have done in other area i.e drivers/usb/storage/uas.c.In gpu drivers assert_spin_locked() make more sense.
Regards Sanjeev Sharma
On Tue, Aug 12, 2014 at 12:25 PM, Daniel Vetter daniel@ffwll.ch wrote:
On Mon, Aug 11, 2014 at 04:38:50PM -0700, David Rientjes wrote:
On Mon, 11 Aug 2014, Rob Clark wrote:
I'm suggesting that if you don't want to incur the cost of the
conditional
everytime you call a certain function with assert_spin_locked() that
you
could covert these to lockdep_assert_held() so the check is only
done when
lockdep is enabled for debugging.
not sure about the nouveau parts, but for the omap and msm hunks, this code getting called at potentially vblank rate (so maybe once or twice per ~16ms).. and lockdep has considerable overhead (for a gpu driver) so I don't always have it enabled. So it sounds like for those two at least assert_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.
-Daniel
Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch