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  1. MariaDB Server
  2. MDEV-32065

Always check whether lock is free at first to optimize InnoDB mutexes

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      `try_lock()` in InnoDB codes is an atomic operation. For example, it's compiled to "lock cmpxchg" in x86. It will force cacheline to be exclusive state and suffer significant performance degradation in heavy contended scenarios when many CPUs `try_lock()`.

      I collected a perf report and it's assembly codes in my benchmark. Attach them in files.

      Look at the TTASEventMutex implementation, for instance. We mark the codes, always check whether lock is free at first, then `try_lock()`.

      old:		while (!try_lock()) {
      		 
      new:		while (!(state() == MUTEX_STATE_UNLOCKED && try_lock())) {

      Based on real real-world workload test on a 224 CPUs x86 server, this change
      brings back 60%+ TPS/perf for MariaDB 10.3.

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          relates to

          Bug - A problem which impairs or prevents the functions of the product. MDEV-21452 Use condition variables and normal mutexes instead of InnoDB os_event and mutex

          • Major - Major loss of function.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. MDEV-24142 rw_lock_t has unnecessarily complex wait logic

          • Major - Major loss of function.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. MDEV-24167 InnoDB unnecessarily uses complex rw-lock implementation

          • Major - Major loss of function.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. MDEV-26467 Unnecessary compare-and-swap loop in futex-based synchronization

          • Major - Major loss of function.
          • Closed

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              marko Marko Mäkelä
              yuhanyang yuhanyang
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