sparc64: speed up etrap/rtrap on NG2 and later processors

For many sun4v processor types, reading or writing a privileged register
has a latency of 40 to 70 cycles.  Use a combination of the low-latency
allclean, otherw, normalw, and nop instructions in etrap and rtrap to
replace 2 rdpr and 5 wrpr instructions and improve etrap/rtrap
performance.  allclean, otherw, and normalw are available on NG2 and
later processors.

The average ticks to execute the flush windows trap ("ta 0x3") with and
without this patch on select platforms:

 CPU            Not patched     Patched    % Latency Reduction

 NG2            1762            1558            -11.58
 NG4            3619            3204            -11.47
 M7             3015            2624            -12.97
 SPARC64-X      829             770              -7.12

Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 43 insertions, 6 deletions

diff --git a/arch/sparc/kernel/etrap_64.S b/arch/sparc/kernel/etrap_64.S
index 1276ca2567ba..5c237467d156 100644
--- a/arch/sparc/kernel/etrap_64.S
+++ b/arch/sparc/kernel/etrap_64.S
@@ -38,7 +38,11 @@ etrap_syscall:	TRAP_LOAD_THREAD_REG(%g6, %g1)
 		or	%g1, %g3, %g1
 		bne,pn	%xcc, 1f
 		 sub	%sp, STACKFRAME_SZ+TRACEREG_SZ-STACK_BIAS, %g2
-		wrpr	%g0, 7, %cleanwin
+661:		wrpr	%g0, 7, %cleanwin
+		.section .fast_win_ctrl_1insn_patch, "ax"
+		.word	661b
+		.word	0x85880000	! allclean
+		.previous
 
 		sethi	%hi(TASK_REGOFF), %g2
 		sethi	%hi(TSTATE_PEF), %g3
@@ -88,16 +92,30 @@ etrap_save:	save	%g2, -STACK_BIAS, %sp
 
 		bne,pn	%xcc, 3f
 		 mov	PRIMARY_CONTEXT, %l4
-		rdpr	%canrestore, %g3
+661:		rdpr	%canrestore, %g3
+		.section .fast_win_ctrl_1insn_patch, "ax"
+		.word	661b
+		nop
+		.previous
+
 		rdpr	%wstate, %g2
-		wrpr	%g0, 0, %canrestore
+661:		wrpr	%g0, 0, %canrestore
+		.section .fast_win_ctrl_1insn_patch, "ax"
+		.word	661b
+		nop
+		.previous
 		sll	%g2, 3, %g2
 
 		/* Set TI_SYS_FPDEPTH to 1 and clear TI_SYS_NOERROR.  */
 		mov	1, %l5
 		sth	%l5, [%l6 + TI_SYS_NOERROR]
 
-		wrpr	%g3, 0, %otherwin
+661:		wrpr	%g3, 0, %otherwin
+		.section .fast_win_ctrl_1insn_patch, "ax"
+		.word	661b
+		.word	0x87880000	! otherw
+		.previous
+
 		wrpr	%g2, 0, %wstate
 		sethi	%hi(sparc64_kern_pri_context), %g2
 		ldx	[%g2 + %lo(sparc64_kern_pri_context)], %g3
diff --git a/arch/sparc/kernel/rtrap_64.S b/arch/sparc/kernel/rtrap_64.S
index 709a82ebd294..dff86fad0a1f 100644
--- a/arch/sparc/kernel/rtrap_64.S
+++ b/arch/sparc/kernel/rtrap_64.S
@@ -224,10 +224,19 @@ rt_continue:	ldx			[%sp + PTREGS_OFF + PT_V9_G1], %g1
 		rdpr			%otherwin, %l2
 		srl			%l1, 3, %l1
 
-		wrpr			%l2, %g0, %canrestore
+661:		wrpr			%l2, %g0, %canrestore
+		.section		.fast_win_ctrl_1insn_patch, "ax"
+		.word			661b
+		.word			0x89880000	! normalw
+		.previous
+
 		wrpr			%l1, %g0, %wstate
 		brnz,pt			%l2, user_rtt_restore
-		 wrpr			%g0, %g0, %otherwin
+661:		 wrpr			%g0, %g0, %otherwin
+		.section		.fast_win_ctrl_1insn_patch, "ax"
+		.word			661b
+		 nop
+		.previous
 
 		ldx			[%g6 + TI_FLAGS], %g3
 		wr			%g0, ASI_AIUP, %asi
diff --git a/arch/sparc/kernel/setup_64.c b/arch/sparc/kernel/setup_64.c
index c4088a3b1051..db4c4d7e28a0 100644
--- a/arch/sparc/kernel/setup_64.c
+++ b/arch/sparc/kernel/setup_64.c
@@ -300,6 +300,11 @@ static void __init sun4v_patch(void)
 		break;
 	}
 
+	if (sun4v_chip_type != SUN4V_CHIP_NIAGARA1) {
+		sun4v_patch_1insn_range(&__fast_win_ctrl_1insn_patch,
+					&__fast_win_ctrl_1insn_patch_end);
+	}
+
 	sun4v_hvapi_init();
 }
 
diff --git a/arch/sparc/kernel/vmlinux.lds.S b/arch/sparc/kernel/vmlinux.lds.S
index 34d37e6c2d06..d78847d56a4b 100644
--- a/arch/sparc/kernel/vmlinux.lds.S
+++ b/arch/sparc/kernel/vmlinux.lds.S
@@ -159,6 +159,11 @@ SECTIONS
 		*(.pud_huge_patch)
 		__pud_huge_patch_end = .;
 	}
+	.fast_win_ctrl_1insn_patch : {
+		__fast_win_ctrl_1insn_patch = .;
+		*(.fast_win_ctrl_1insn_patch)
+		__fast_win_ctrl_1insn_patch_end = .;
+	}
 	PERCPU_SECTION(SMP_CACHE_BYTES)
 
 #ifdef CONFIG_JUMP_LABEL