Documentation/metag/cachepart.txt

Meta Cache Partitioning
=======================

The cachepart functions are for manipulating the local and global per hardware
thread cache partitions. See arch/metag/include/asm/cachepart.h for the
documentation of the functions.

The main use of this at the moment is to make sure that the current thread has a
global cache partition that is big enough to hold locked in core cache during a
standby (see coremem.txt for more information).


cachepart_min_iglobal
---------------------

This function rearranges the current thread's cache partitions so that global
cache is available, specifically private global cache if CACHEPART_PRIV_GLOBAL
is specified in the flags (e.g. for use by locked in core cache mode). If the
rearrangement would violate the constraints of the architecture, for example by
having a cache partition that is too small, or smaller than the requested size,
an error code is returned and nothing is changed. For example, if the icache is
mapped like this:

0          1/4         1/2         3/4          1
+-----------+-----------+-----------------------+
| T0 local  | T1 local  | T0/T1 global          |
+-----------+-----------+-----------------------+

It would be rearranged to the following when called from T0 with the PRIV_GLOBAL
flag:

0    1/8   1/4         1/2         3/4          1
+-----+-----+-----------+-----------------------+
| T0L | T0G | T1 local  | T1 global             |
+-----+-----+-----------+-----------------------+

And would be left alone without the PRIV_GLOBAL flag (since T0's global
partition is likely already big enough). Upon calling cachepart_restore_iglobal,
the cache partitions would be restored to their previous layout.