Write FIFO - write requests stored chronologically.Read FIFO - read requests stored chronologically.This fixes starvation issues seen in other schedulers. NOTE: Non-multiqueue have been deprecated in Ubuntu Eoan Ermine 19.10 onwards as they are no longer supported in the Linux 5.3 kernel. A good all-rounder with fairly low CPU overhead. This is an adaption of the deadline I/O scheduler but designed for Multiqueue devices. Ideal for fast random I/O devices such as NVME. Does no reordering of requests, minimal overhead. In theory this limits the time waiting for requests to be dispatched, and hence should provide quick completion time for requests that are high priority. There are strict limits on the number of request operations sent to the queues. Desktop users may like to experiment with this I/O scheduler as it can be advantageous when loading large applications.ĭesigned for fast multi-queue devices and is relatively simple. Fair sharing is based on the number of sectors requested and heuristics rather than a time slice. This is a complex I/O scheduler and has a relatively high per-operation overhead so it is not ideal for devices with slow CPUs or high throughput I/O devices. These map I/O requests to multiple queues and these are handled by kernel threads that are distributed across multiple CPUs.ĭesigned to provide good interactive response, especially for slower I/O devices. The following I/O schedulers are designed for multiqueue devices. Note: These are the only I/O schedulers available in Ubuntu Eoan Ermine 19.10 and onwards. I/O schedulers attempt to balance the need for high throughput while trying to fairly share I/O requests amongst processes.ĭifferent approaches have been taken for various I/O schedulers and each has their own set of strengths and weaknesses and the general rule is that there is no perfect default I/O scheduler for all the range of I/O demands a system may experience. While this may increase overall throughput it may lead to some I/O requests waiting for too long, causing latency issues. I/O schedulers attempt to improve throughput by reordering request access into a linear order based on the logical addresses of the data and trying to group these together.
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