DM-Crypt Adding "High Priority" Option In Linux 6.10

Written by Michael Larabel in Linux Storage on 1 May 2024 at 05:00 AM EDT. 1 Comment
Queued up as part of the DeviceMapper dm-crypt changes for Linux 6.10 is adding a new "high priority" option.

The Linux kernel's dm-crypt code for transparent block device encryption will be honoring a "high_priority" option come Linux 6.10. Setting the "high_priority" option will set dm-crypt workqueues and the writer thread to high priority in order to improve throughput and latency but at the cost of degraded responsiveness of the system.

dm-crypt high_priority text

The patch by Red Hat's Mikulas Patocka explains:
"When WQ_HIGHPRI was used for the dm-crypt kcryptd workqueue it was reported that dm-crypt performs badly when the system is loaded. Because of reports of audio skipping, dm-crypt stopped using WQ_HIGHPRI with commit f612b2132db5 (Revert "dm crypt: use WQ_HIGHPRI for the IO and crypt workqueues").

But it has since been determined that WQ_HIGHPRI provides improved performance (with reduced latency) for highend systems with much more resources than those laptop/desktop users which suffered from the use of WQ_HIGHPRI.

As such, add an option "high_priority" that allows the use of WQ_HIGHPRI for dm-crypt's workqueues and also sets the write_thread to nice level MIN_NICE (-20). This commit makes it optional, so that normal users won't be harmed by it."

Thus with this patch in DeviceMapper's for-next / dm-6.10 branch is the optional support for higher-end systems to set the "high_priority" option to enjoy higher throughput and better latency. But those on lower-tier hardware likely will be better off without using it. The Linux 6.10 merge window will be opening up in mid-May.
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