MIPS: Take in account load hazards for HI/LO restoring
PATCH v2 1/1 MIPS: Take in account load hazards for HI/LO restoring
MIPS CPUs usually have 1 to 4 cycles load hazards, thus doing load and right after move to HI/LO will usually stall the pipeline for significant amount of time. Let's take it into account and separate loads and mthi/lo in instruction sequence.
The patch uses t6 and t7 registers as temporaries in addition to t8.
The patch tries to deal with SmartMIPS, but I know little about and haven't tested it.
Changes in v2:
- clear separation of actions for SmartMIPS and pre-MIPSR6.
--- arch/mips/include/asm/stackframe.h | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-)
arch/mips/include/asm/stackframe.h +11 -8
@@ -308,17 +308,12 @@ jal octeon_mult_restore#endif #ifdef CONFIG_CPU_HAS_SMARTMIPS - LONG_L $24, PT_ACX(sp) - mtlhx $24 - LONG_L $24, PT_HI(sp) - mtlhx $24 + LONG_L $14, PT_ACX(sp) LONG_L $24, PT_LO(sp) - mtlhx $24 + LONG_L $15, PT_HI(sp)#elif !defined(CONFIG_CPU_MIPSR6 ) LONG_L $24, PT_LO(sp) - mtlo $24 - LONG_L $24, PT_HI(sp) - mthi $24 + LONG_L $15, PT_HI(sp)#endif #ifdef CONFIG_32BIT cfi_ld $8, PT_R8, \docfi
@@ -327,6 +322,14 @@ cfi_ld $10, PT_R10, \docfi cfi_ld $11, PT_R11, \docfi cfi_ld $12, PT_R12, \docfi +#ifdef CONFIG_CPU_HAS_SMARTMIPS + mtlhx $14 + mtlhx $15 + mtlhx $24 +#elif !defined(CONFIG_CPU_MIPSR6) + mtlo $24 + mthi $15 +#endif cfi_ld $13, PT_R13, \docfi cfi_ld $14, PT_R14, \docfi cfi_ld $15, PT_R15, \docfi
Signature · 1 line
2.44.0
Quoted 10 lines · Siarhei Volkau
MIPS CPUs usually have 1 to 4 cycles load hazards, thus doing load and right after move to HI/LO will usually stall the pipeline for significant amount of time. Let's take it into account and separate loads and mthi/lo in instruction sequence.
The patch uses t6 and t7 registers as temporaries in addition to t8.
The patch tries to deal with SmartMIPS, but I know little about and haven't tested it.
Quoted 8 lines
Changes in v2:
- clear separation of actions for SmartMIPS and pre-MIPSR6.Signed-off-by Siarhei Volkau <[email protected]>--- arch/mips/include/asm/stackframe.h | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-)
applied to mips-next.
Thomas.
Signature · 2 lines
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]