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When using a kthread to delay the IOs, dm-delay would continuously loop, checking if IOs were ready to submit. It had a cond_resched() call in the loop, but might still loop hundreds of millions of times waiting for an IO that was scheduled to be submitted 10s of ms in the future. With the change to make dm-delay over zoned devices always use kthreads regardless of the length of the delay, this wasted work only gets worse. To solve this and still keep roughly the same precision for very short delays, dm-delay now calls fsleep() for 1/8th of the smallest non-zero delay it will place on IOs, or 1 ms, whichever is smaller. The reason that dm-delay doesn't just use the actual expiration time of the next delayed IO to calculated the sleep time is that delay_dtr() must wait for the kthread to finish before deleting the table. If a zoned device with a long delay queued an IO shortly before being suspended and removed, the IO would be flushed in delay_presuspend(), but the removing the device would still have to wait for the remainder of the long delay. This time is now capped at 1 ms. Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com> Reviewed-by: Damien Le Moal <dlemoal@kernel.org> Tested-by: Damien Le Moal <dlemoal@kernel.org> Signed-off-by: Mikulas Patocka <mpatocka@redhat.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 reStructuredText 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.