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

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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>
This commit is contained in:
Michael Neuling
2015-12-11 09:34:42 +11:00
committed by Michael Ellerman
parent c395465da6
commit 2fc251a8dd
3 changed files with 22 additions and 8 deletions
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8
arch/powerpc/kernel/asm-offsets.c
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@@ -186,12 +186,12 @@ int main(void)
DEFINE(PACASOFTIRQEN, offsetof(struct paca_struct, soft_enabled));
DEFINE(PACAIRQHAPPENED, offsetof(struct paca_struct, irq_happened));
#ifdef CONFIG_PPC_BOOK3S
DEFINE(PACACONTEXTID, offsetof(struct paca_struct, context.id));
DEFINE(PACACONTEXTID, offsetof(struct paca_struct, mm_ctx_id));
#ifdef CONFIG_PPC_MM_SLICES
DEFINE(PACALOWSLICESPSIZE, offsetof(struct paca_struct,
context.low_slices_psize));
mm_ctx_low_slices_psize));
DEFINE(PACAHIGHSLICEPSIZE, offsetof(struct paca_struct,
context.high_slices_psize));
mm_ctx_high_slices_psize));
DEFINE(MMUPSIZEDEFSIZE, sizeof(struct mmu_psize_def));
#endif /* CONFIG_PPC_MM_SLICES */
#endif
@@ -224,7 +224,7 @@ int main(void)
#ifdef CONFIG_PPC_MM_SLICES
DEFINE(MMUPSIZESLLP, offsetof(struct mmu_psize_def, sllp));
#else
DEFINE(PACACONTEXTSLLP, offsetof(struct paca_struct, context.sllp));
DEFINE(PACACONTEXTSLLP, offsetof(struct paca_struct, mm_ctx_sllp));
#endif /* CONFIG_PPC_MM_SLICES */
DEFINE(PACA_EXGEN, offsetof(struct paca_struct, exgen));
DEFINE(PACA_EXMC, offsetof(struct paca_struct, exmc));