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__; \
+ for (;;) { \
+ if (time_after(jiffies, timeout__)) \
+ ret__ = -ETIMEDOUT; \
+ if (COND) { \
+ ret__ = 0; \
break; \
} \
+ if (ret__) \
+ break; \
if ((W) && drm_can_sleep()) { \
usleep_range((W), (W)*2); \
} else { \
--
2.9.3
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