tree c851eab2210153cfc4e706b2680ef64ee2329dce
parent c395465da68bfc3a238d5bc15f862e33e6e9ecec
author Michael Neuling <mikey@neuling.org> 1449786882 +1100
committer Michael Ellerman <mpe@ellerman.id.au> 1451203934 +1100

powerpc: Copy only required pieces of the mm_context_t to the paca

Currently we copy the whole mm_context_t to the paca but only access a
few bits of it.  This is wasteful of space paca and also takes quite
some time in the hot path of context switching.

This patch pulls in only the required bits from the mm_context_t to
the paca and on context switch, copies only those.

Benchmarking this (On top of Anton's recent MSR context switching
changes [1]) using processes and yield shows an improvement of almost
3% on POWER8:

  http://ozlabs.org/~anton/junkcode/context_switch2.c
  ./context_switch2 --test=yield --process 0 0

1. https://lists.ozlabs.org/pipermail/linuxppc-dev/2015-October/135700.html

Signed-off-by: Michael Neuling <mikey@neuling.org>
[mpe: Rename paca fields to be mm_ctx_foo rather than context_foo]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>