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During suspend, Linus found that his machine would hang for 3 seconds, and identified that intel_ring_buffer_wait() was the culprit: "Because from looking at the code, I get the notion that "intel_read_status_page()" may not be exact. But what happens if that inexact value matches our cached ring->actual_head, so we never even try to read the exact case? Does it _stay_ inexact for arbitrarily long times? If so, we might wait for the ring to empty forever (well, until the timeout - the behavior I see), even though the ring really _is_ empty." As the reported HEAD position is only updated every time it crosses a 64k boundary, whilst draining the ring it is indeed likely to remain one value. If that value matches the last known HEAD position, we never read the true value from the register and so trigger a timeout. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> |
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