Commit cf0a8aa0 authored by Markos Chandras's avatar Markos Chandras Committed by Ralf Baechle
Browse files

MIPS: cpu-probe: Set the FTLB probability bit on supported cores 



Make use of the Config6/FLTBP bit to set the probability of a TLBWR
instruction to hit the FTLB or the VTLB. A value of 0 (which may be
the default value on certain cores, such as proAptiv or P5600)
means that a TLBWR instruction will never hit the VTLB which
leads to performance limitations since it effectively decreases
the number of available TLB slots.

Signed-off-by: default avatarMarkos Chandras <markos.chandras@imgtec.com>
Reviewed-by: default avatarJames Hogan <james.hogan@imgtec.com>
Cc: <stable@vger.kernel.org> # v3.15+
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8368/


Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 4ec8f9e9

arch/mips/include/asm/mipsregs.h

+2 −0
Original line number Diff line number Diff line
@@ -661,6 +661,8 @@ 
#define MIPS_CONF6_SYND		(_ULCAST_(1) << 13)

/* proAptiv FTLB on/off bit */

#define MIPS_CONF6_FTLBEN	(_ULCAST_(1) << 15)

/* FTLB probability bits */

#define MIPS_CONF6_FTLBP_SHIFT	(16)



#define MIPS_CONF7_WII		(_ULCAST_(1) << 31)

arch/mips/kernel/cpu-probe.c

+32 −1
Original line number Diff line number Diff line
@@ -193,6 +193,32 @@ static void set_isa(struct cpuinfo_mips *c, unsigned int isa) 
static char unknown_isa[] = KERN_ERR \

	"Unsupported ISA type, c0.config0: %d.";



static unsigned int calculate_ftlb_probability(struct cpuinfo_mips *c)

{



	unsigned int probability = c->tlbsize / c->tlbsizevtlb;



	/*

	 * 0 = All TLBWR instructions go to FTLB

	 * 1 = 15:1: For every 16 TBLWR instructions, 15 go to the

	 * FTLB and 1 goes to the VTLB.

	 * 2 = 7:1: As above with 7:1 ratio.

	 * 3 = 3:1: As above with 3:1 ratio.

	 *

	 * Use the linear midpoint as the probability threshold.

	 */

	if (probability >= 12)

		return 1;

	else if (probability >= 6)

		return 2;

	else

		/*

		 * So FTLB is less than 4 times bigger than VTLB.

		 * A 3:1 ratio can still be useful though.

		 */

		return 3;

}



static void set_ftlb_enable(struct cpuinfo_mips *c, int enable)

{

	unsigned int config6;
@@ -203,9 +229,14 @@ static void set_ftlb_enable(struct cpuinfo_mips *c, int enable) 
	case CPU_P5600:

		/* proAptiv & related cores use Config6 to enable the FTLB */

		config6 = read_c0_config6();

		/* Clear the old probability value */

		config6 &= ~(3 << MIPS_CONF6_FTLBP_SHIFT);

		if (enable)

			/* Enable FTLB */

			write_c0_config6(config6 | MIPS_CONF6_FTLBEN);

			write_c0_config6(config6 |

					 (calculate_ftlb_probability(c)

					  << MIPS_CONF6_FTLBP_SHIFT)

					 | MIPS_CONF6_FTLBEN);

		else

			/* Disable FTLB */

			write_c0_config6(config6 &  ~MIPS_CONF6_FTLBEN);

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