On Tue, Sep 13, 2016 at 08:40:19PM +0100, Chris Wilson wrote:
> I was looking at some wait_for() timeouts on a slow system, with lots of
> debug enabled (KASAN, lockdep, mmio_debug). Thinking that we were
> mishandling the timeout, I tried to ensure that we loop at least once
> after first testing COND. However, the double test of COND either side
> of the timeout check makes that unlikely. But we can do an equivalent
> loop, that keeps the COND check after testing for timeout (required so
> that we are not preempted between testing COND and then testing for a
> timeout) without expanding COND twice.
>
> The advantage of only expanding COND once is a dramatic reduction in
> code size:
>
> text data bss dec hex
> 1308733 5184 1152 1315069 1410fd before
> 1305341 5184 1152 1311677 1403bd after
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_drv.h | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index cb99a2540863..597899d71df9 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -52,13 +52,16 @@
> */
> #define _wait_for(COND, US, W) ({ \
> unsigned long timeout__ = jiffies + usecs_to_jiffies(US) + 1; \
> - int ret__ = 0; \
> - while (!(COND)) { \
> - if (time_after(jiffies, timeout__)) { \
> - if (!(COND)) \
> - ret__ = -ETIMEDOUT; \
> + int ret__; \
Ok, this is the magic. Missed initializer, gcc goes wild trimming
undefined code. Patch is completely bogus.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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