# Different cpu consumption by scylla threads with different linux kernels after the "nodetool drain" command

**URL:** <https://forum.scylladb.com/t/different-cpu-consumption-by-scylla-threads-with-different-linux-kernels-after-the-nodetool-drain-command/494>\
**Category:** ScyllaDB\
**Created:** [April 30, 2023, 9:15am UTC](https://forum.scylladb.com/t/different-cpu-consumption-by-scylla-threads-with-different-linux-kernels-after-the-nodetool-drain-command/494 "2023-04-30T09:15:47Z")\
**Posts on this page:** 1\
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**Author:** ![Botond\_Denes](https://sea2.discourse-cdn.com/flex016/user_avatar/forum.scylladb.com/botond_denes/32/163_2.png) [@Botond\_Denes](https://forum.scylladb.com/u/Botond_Denes)\
**Post date:** [May 3, 2023, 4:26am UTC](https://forum.scylladb.com/t/different-cpu-consumption-by-scylla-threads-with-different-linux-kernels-after-the-nodetool-drain-command/494/2 "2023-05-03T04:26:49Z")

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The answer is in the `strace` output. On the older kernels ScyllaDB falls back to use `epoll` for polling the kernel for I/O. This is not as efficient and involves the DB busy-polling the kernel, hence the 100% CPU usage, even when idle.  
On newer kernels, where it is available, ScyllaDB will use the AIO kernel interface to poll for I/O completion, which is much more efficient.

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