39823d0fac
Because we use a single work structure attached to the CIL rather than the CIL context, we can only queue a single work item at a time. This results in the CIL being single threaded and limits performance when it becomes CPU bound. The design of the CIL is that it is pipelined and multiple commits can be running concurrently, but the way the work is currently implemented means that it is not pipelining as it was intended. The critical work to switch the CIL context can take a few milliseconds to run, but the rest of the CIL context flush can take hundreds of milliseconds to complete. The context switching is the serialisation point of the CIL, once the context has been switched the rest of the context push can run asynchrnously with all other context pushes. Hence we can move the work to the CIL context so that we can run multiple CIL pushes at the same time and spread the majority of the work out over multiple CPUs. We can keep the per-cpu CIL commit state on the CIL rather than the context, because the context is pinned to the CIL until the switch is done and we aggregate and drain the per-cpu state held on the CIL during the context switch. However, because we no longer serialise the CIL work, we can have effectively unlimited CIL pushes in progress. We don't want to do this - not only does it create contention on the iclogs and the state machine locks, we can run the log right out of space with outstanding pushes. Instead, limit the work concurrency to 4 concurrent works being processed at a time. This is enough concurrency to remove the CIL from being a CPU bound bottleneck but not enough to create new contention points or unbound concurrency issues. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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.