754a254427
If we are already in the desired write domain of a set-domain ioctl,
then there is nothing for us to do and we can quickly return back to
userspace, avoiding any lock contention. By recognising that the
write_domain is always a subset of the read_domains, and excluding the
no-op case of requiring 0 read_domains in the ioctl, we can infer if the
current write_domain matches the target read_domains, there is nothing
for us to do.
Secondary aspect of this is that we undo the arbitrary fetching and
potential flushing of all pages for a set-domain(.write=CPU) call on a
fresh object -- which was introduced simply because we do the get-pages
before taking the struct_mutex.
References: 40e62d5d6be8 ("drm/i915: Acquire the backing storage outside of struct_mutex in set-domain")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Reviewed-by: Matthew Auld <matthew.william.auld@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190321161908.8007-2-chris@chris-wilson.co.uk
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.