c40f63790e
Currently links are always done in an async fashion, unless we catch them inline after we successfully complete a request without having to resort to blocking. This isn't necessarily the most efficient approach, it'd be more ideal if we could just use the task_work handling for this. Outside of saving an async jump, we can also do less prep work for these kinds of requests. Running dependent links from the task_work handler yields some nice performance benefits. As an example, examples/link-cp from the liburing repository uses read+write links to implement a copy operation. Without this patch, the a cache fold 4G file read from a VM runs in about 3 seconds: $ time examples/link-cp /data/file /dev/null real 0m2.986s user 0m0.051s sys 0m2.843s and a subsequent cache hot run looks like this: $ time examples/link-cp /data/file /dev/null real 0m0.898s user 0m0.069s sys 0m0.797s With this patch in place, the cold case takes about 2.4 seconds: $ time examples/link-cp /data/file /dev/null real 0m2.400s user 0m0.020s sys 0m2.366s and the cache hot case looks like this: $ time examples/link-cp /data/file /dev/null real 0m0.676s user 0m0.010s sys 0m0.665s As expected, the (mostly) cache hot case yields the biggest improvement, running about 25% faster with this change, while the cache cold case yields about a 20% increase in performance. Outside of the performance increase, we're using less CPU as well, as we're not using the async offload threads at all for this anymore. Signed-off-by: Jens Axboe <axboe@kernel.dk>
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.