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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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18
arch/powerpc/include/asm/paca.h
View file

@ -16,6 +16,7 @@
#ifdef CONFIG_PPC64
#include <linux/string.h>
#include <asm/types.h>
#include <asm/lppaca.h>
#include <asm/mmu.h>
@ -132,7 +133,13 @@ struct paca_struct {
#endif /* CONFIG_PPC_BOOK3E */
#ifdef CONFIG_PPC_BOOK3S
mm_context_t context;
mm_context_id_t mm_ctx_id;
#ifdef CONFIG_PPC_MM_SLICES
u64 mm_ctx_low_slices_psize;
unsigned char mm_ctx_high_slices_psize[SLICE_ARRAY_SIZE];
#else
u16 mm_ctx_sllp;
#endif
#endif
/*
@ -199,7 +206,14 @@ struct paca_struct {
#ifdef CONFIG_PPC_BOOK3S
static inline void copy_mm_to_paca(mm_context_t *context)
{
get_paca()->context = *context;
get_paca()->mm_ctx_id = context->id;
#ifdef CONFIG_PPC_MM_SLICES
get_paca()->mm_ctx_low_slices_psize = context->low_slices_psize;
memcpy(&get_paca()->mm_ctx_high_slices_psize,
&context->high_slices_psize, SLICE_ARRAY_SIZE);
#else
get_paca()->mm_ctx_sllp = context->sllp;
#endif
}
#else
static inline void copy_mm_to_paca(mm_context_t *context){}

8
arch/powerpc/kernel/asm-offsets.c
View file

@ -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));

4
arch/powerpc/mm/hash_utils_64.c
View file

@ -853,11 +853,11 @@ static unsigned int get_paca_psize(unsigned long addr)
unsigned long index, mask_index;
if (addr < SLICE_LOW_TOP) {
lpsizes = get_paca()->context.low_slices_psize;
lpsizes = get_paca()->mm_ctx_low_slices_psize;
index = GET_LOW_SLICE_INDEX(addr);
return (lpsizes >> (index * 4)) & 0xF;
}
hpsizes = get_paca()->context.high_slices_psize;
hpsizes = get_paca()->mm_ctx_high_slices_psize;
index = GET_HIGH_SLICE_INDEX(addr);
mask_index = index & 0x1;
return (hpsizes[index >> 1] >> (mask_index * 4)) & 0xF;