Fastboot: aszinkron függvényhívások a kernel boot idejének csökkentése érdekében

Jelenleg a kernel boot nagy része szinkron módon zajlik és ez nem valami gyors, mert a hardverek inicializálásából származó késedelmek egymást követően jelentkeznek. Annak érdekében, hogy a kernel gyorsabban bootoljon, a patchset egy olyan mechanizmust vezet be, amely lehetővé teszi egyes inicializációs lépések aszinkron végrehajtását, s ez a gyakorlatban "elrejti" az ebből adódó késedelmek egy jelentős részét.

Idézet a patch-ből:

Goals and Theory of Operation

The primary goal of this feature is to reduce the kernel boot time,
by doing various independent hardware delays and discovery operations
decoupled and not strictly serialized.

More specifically, the asynchronous function call concept allows
certain operations (primarily during system boot) to happen
asynchronously, out of order, while these operations still
have their externally visible parts happen sequentially and in-order.
(not unlike how out-of-order CPUs retire their instructions in order)

Key to the asynchronous function call implementation is the concept of
a "sequence cookie" (which, although it has an abstracted type, can be
thought of as a monotonically incrementing number).

The async core will assign each scheduled event such a sequence cookie and
pass this to the called functions.

The asynchronously called function should before doing a globally visible
operation, such as registering device numbers, call the
async_synchronize_cookie() function and pass in its own cookie. The
async_synchronize_cookie() function will make sure that all asynchronous
operations that were scheduled prior to the operation corresponding with the
cookie have completed.

Subsystem/driver initialization code that scheduled asynchronous probe
functions, but which shares global resources with other drivers/subsystems
that do not use the asynchronous call feature, need to do a full
synchronization with the async_synchronize_full() function, before returning
from their init function. This is to maintain strict ordering between the
asynchronous and synchronous parts of the kernel.

A bejelentés itt olvasható.