On 01/02/16 14:15, Tvrtko Ursulin wrote:
On 01/02/16 13:30, Chris Wilson wrote:
On Mon, Feb 01, 2016 at 01:17:35PM +0000, Tvrtko Ursulin wrote:
From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Currently the wait_for_atomic_us only allows for a millisecond
granularity which is not nice towards callers requesting small
micro-second waits.
Re-implement it so micro-second granularity is really supported
and not just in the name of the macro.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
Danger - this might break things which currently work by accident!
---
drivers/gpu/drm/i915/intel_drv.h | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_drv.h
b/drivers/gpu/drm/i915/intel_drv.h
index f620023ed134..9e8a1202194c 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -63,10 +63,25 @@
ret__; \
})
+#define _wait_for_atomic(COND, US) ({ \
+ unsigned long end__; \
+ int ret__ = 0; \
+ get_cpu(); \
Hmm, by virtue of its name (and original intent), we are expected to be
in an atomic context and could just do a BUG_ON(!in_atomic()) to catch
misuse. Since the removal of the panic modeset, all callers outside of
intel_uncore.c are definitely abusing this and we would be better to use
a usleep[_range]() variant instead.
I considered a WARN_ON_ONCE and a BUILD_BUG_ON for very long waits but
chickened out on both.
I'll respin with a WARN_ON_ONCE(!in_atomic)) to start with.
Can't really do that it seems since in_atomic() will be always false on
non-fully-preemptible kernels.
Could do the current cpu comparison trick to catch false timeouts due
callers from non-atomic sections but not sure if it is worth it. So it
looks like manual audit of call sites to me.
Or find a time source with micro-second resolution which does not go
backwards on CPU migrations?
Regards,
Tvrtko
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