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b8a1c2380b
by only storing a word in each thread context, we can keep the history of all taken/dropped locks by label. This is expected to be very cheap and to permit to store up to 8 consecutive lock operations in 64 bits. That should significantly help detect recursive locks as well as figure what thread was likely to hinder another one waiting for a lock. For now we only store the final state of the lock, we don't store the attempt to get it. It's just a matter of space since we already need 4 ops (rd,sk,wr,un) which take 2 bits, leaving max 64 labels. We're already around 45. We could also multiply by 5 and still keep 8 bits total per lock, that would limit us to 51 locks max. It seems that most of the time if we get a watchdog panic, anyway the victim thread will be perfectly located so that we don't need a specific value for this. Another benefit is that we perform a single memory write per lock. |
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