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Commit 2fc251a8 authored by Michael Neuling's avatar Michael Neuling Committed by Michael Ellerman
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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: default avatarMichael Neuling <mikey@neuling.org>
[mpe: Rename paca fields to be mm_ctx_foo rather than context_foo]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent c395465d

arch/powerpc/include/asm/paca.h

+16 −2
Original line number Diff line number Diff line
@@ -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){}

arch/powerpc/kernel/asm-offsets.c

+4 −4
Original line number Diff line number Diff line
@@ -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));

arch/powerpc/mm/hash_utils_64.c

+2 −2
Original line number Diff line number Diff line
@@ -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;