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c1b5869bab
Most of dsl_dir_diduse_space() and dsl_dir_transfer_space() CPU time is a dd_lock overhead and time spent in dmu_buf_will_dirty(). Calling them one after another is a waste of time and even more contention. Doing that twice for each rewritten block within dbuf_write_done() via dsl_dataset_block_kill() and dsl_dataset_block_born() created one of the biggest CPU overheads in case of small blocks rewrite. dsl_dir_diduse_transfer_space() combines functionality of these two functions for cases where it is needed, but without double overhead, practically for the cost of dsl_dir_diduse_space() or even cheaper. While there, optimize dsl_dir_phys() calls in dsl_dir_diduse_space() and dsl_dir_transfer_space(). It seems Clang detects some aliasing there, repeating dd->dd_dbuf->db_data dereference multiple times, increasing dd_lock scope and contention. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Matthew Ahrens <mahrens@delphix.com> Author: Ryan Moeller <ryan@iXsystems.com> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Sponsored-By: iXsystems, Inc. Closes #12300 |
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