当系统管理员听到可能出现了磁盘争用问题时，他或她首先会求助于iostat。
When a system administrator hears that there might be a disk contention issue, the first thing he or she turns to is iostat.
如果同步时还发生锁定争用，那么性能上付出的代价会大得多，因为会需要几个线程切换和系统调用。
If the synchronization actually requires contending for the lock, the performance penalty is substantially greater, as there will be several thread switches and system calls required.
争用同步之所以慢，是因为它涉及多个线程切换和系统调用。
Contended synchronizations are slow because they involve multiple thread switches and system calls.
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