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The write back throttling (WBT) code checks if REQ_SYNC | REQ_IDLE is set to determine if a write is O_DIRECT vs buffered. If the bits are not set then it assumes it's a buffered write and will throttle LIO if we hit certain metrics. LIO itself is not using the buffer cache and is doing direct I/O, so this has us set the direct bits so we are not throttled. When the initiator application is doing direct I/O this can greatly improve performance. It depends on the backend device but we have seen where the WBT code is throttling writes to only 20K IOPs with 4K I/Os when the device can support 100K+. Signed-off-by: Mike Christie <michael.christie@oracle.com> Link: https://lore.kernel.org/r/20230817192902.346791-1-michael.christie@oracle.com Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.