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drm/i915: Only expand COND once in wait_for()

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Commentary from Chris Wilson's original version:

> 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

but it turned out that due to a missing iniitialiser, gcc had "gone
wild trimming undefined code" :( This version acheives a rather more
modest (but still worthwhile) gain of ~550 bytes.

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Original-idea-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Zanoni, Paulo R <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1473855033-26980-1-git-send-email-david.s.gordon@intel.com
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
This commit is contained in:
Dave Gordon 2016-09-14 13:10:33 +01:00 committed by Chris Wilson
parent c8ebfad7a0
commit b0876afdff
1 changed files with 9 additions and 5 deletions
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14
drivers/gpu/drm/i915/intel_drv.h
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@ -52,11 +52,15 @@
*/ */
#define _wait_for(COND, US, W) ({ \ #define _wait_for(COND, US, W) ({ \
unsigned long timeout__ = jiffies + usecs_to_jiffies(US) + 1; \ unsigned long timeout__ = jiffies + usecs_to_jiffies(US) + 1; \
int ret__ = 0; \ int ret__; \
while (!(COND)) { \ for (;;) { \
if (time_after(jiffies, timeout__)) { \ bool expired__ = time_after(jiffies, timeout__); \
if (!(COND)) \ if (COND) { \
ret__ = -ETIMEDOUT; \ ret__ = 0; \
break; \
} \
if (expired__) { \
ret__ = -ETIMEDOUT; \
break; \ break; \
} \ } \
if ((W) && drm_can_sleep()) { \ if ((W) && drm_can_sleep()) { \