7261fc2e81
For each WRITE record in the stream, `zfs receive` creates a DMU transaction (`dmu_tx_create()`) and writes this block's data into the object. If per-block overheads (as opposed to per-byte overheads) dominate performance (as is often the case with small recordsize), the per-dmu-transaction overheads can be significant. For example, in some workloads the `receieve_writer` thread is 100% on CPU, and more than half of its CPU time is in these per-tx routines (e.g. dmu_tx_hold_write, dmu_tx_assign, dmu_tx_commit). To improve performance of `zfs receive`, this commit batches WRITE records which are to nearby offsets of the same object, and uses one DMU transaction to write them all. By default the batch size is 1MB, which for recordsize=8K reduces the number of DMU transactions by 128x for full send streams (incrementals will depend on how "clumpy" the changed blocks are). This commit improves the performance of `dd if=stream | zfs recv` from 78,800 blocks/sec to 98,100 blocks/sec (25% improvement). Reviewed-by: Paul Dagnelie <pcd@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> Closes #10099 |
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