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.