[PATCH 3.17 007/122] MIPS: cpu-probe: Set the FTLB probability bit on supported cores

From: Greg Kroah-Hartman
Date: Fri Dec 05 2014 - 18:50:24 EST


3.17-stable review patch. If anyone has any objections, please let me know.

------------------

From: Markos Chandras <markos.chandras@xxxxxxxxxx>

commit cf0a8aa0226da5de88011e7f30eff22a894b2f49 upstream.

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: Markos Chandras <markos.chandras@xxxxxxxxxx>
Reviewed-by: James Hogan <james.hogan@xxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Patchwork: https://patchwork.linux-mips.org/patch/8368/
Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
arch/mips/include/asm/mipsregs.h | 2 ++
arch/mips/kernel/cpu-probe.c | 33 ++++++++++++++++++++++++++++++++-
2 files changed, 34 insertions(+), 1 deletion(-)

--- a/arch/mips/include/asm/mipsregs.h
+++ b/arch/mips/include/asm/mipsregs.h
@@ -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)

--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -192,6 +192,32 @@ static void set_isa(struct cpuinfo_mips
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;
@@ -202,9 +228,14 @@ static void set_ftlb_enable(struct cpuin
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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