A log cache block holds log records for the database. Many workers are allowed to add log records to the same log cache buffer (LC) in parallel. When the log cache block becomes full, or a commit request requires the block to be saved to stable media the log cache buffer is ‘flushed.’
SQL Server optimizes database log file flush requests, performing these flush requests inline on the active worker. Certain patterns of log record activity may encounter increased spinlock contention while performing the log cache block flush activities.
Trace flag -T8409 (startup only trace flag) disables inline log