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@xxxxxxxxx>
Original-idea-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Zanoni, Paulo R <paulo.r.zanoni@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_drv.h | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index abe7a4d..8fd16ad 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -52,11 +52,15 @@
*/
#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__; \
+ for (;;) { \
+ bool expired__ = time_after(jiffies, timeout__); \
+ if (COND) { \
+ ret__ = 0; \
+ break; \
+ } \
+ if (expired__) { \
+ ret__ = -ETIMEDOUT; \
break; \
} \
if ((W) && drm_can_sleep()) { \
--
1.9.1
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