[PATCH] powerpc: Fix runlatch performance issues

The runlatch SPR can take a lot of time to write. My original runlatch
code would set it on every exception entry even though most of the time
this was not required. It would also continually set it in the idle
loop, which is an issue on an SMT capable processor.

Now we cache the runlatch value in a threadinfo bit, and only check for
it in decrementer and hardware interrupt exceptions as well as the idle
loop. Boot on POWER3, POWER5 and iseries, and compile tested on pmac32.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

2 files changed, 34 insertions, 10 deletions

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 2b03a09fe5e9..bb845eed0e98 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -319,7 +319,6 @@ exception_marker:
 label##_pSeries:                                        \
         HMT_MEDIUM;                                     \
         mtspr   SPRN_SPRG1,r13;         /* save r13 */  \
-        RUNLATCH_ON(r13);                               \
         EXCEPTION_PROLOG_PSERIES(PACA_EXGEN, label##_common)
 
 #define STD_EXCEPTION_ISERIES(n, label, area)           \
@@ -327,7 +326,6 @@ label##_pSeries:					\
 label##_iSeries:                                        \
         HMT_MEDIUM;                                     \
         mtspr   SPRN_SPRG1,r13;         /* save r13 */  \
-        RUNLATCH_ON(r13);                               \
         EXCEPTION_PROLOG_ISERIES_1(area);               \
         EXCEPTION_PROLOG_ISERIES_2;                     \
         b       label##_common
@@ -337,7 +335,6 @@ label##_iSeries:					\
 label##_iSeries:                                                        \
         HMT_MEDIUM;                                                     \
         mtspr   SPRN_SPRG1,r13;         /* save r13 */                  \
-        RUNLATCH_ON(r13);                                               \
         EXCEPTION_PROLOG_ISERIES_1(PACA_EXGEN);                         \
         lbz     r10,PACAPROCENABLED(r13);                               \
         cmpwi   0,r10,0;                                                \
@@ -390,6 +387,7 @@ label##_common:						\
 label##_common:                                         \
         EXCEPTION_PROLOG_COMMON(trap, PACA_EXGEN);      \
         DISABLE_INTS;                                   \
+        bl      .ppc64_runlatch_on;                     \
         addi    r3,r1,STACK_FRAME_OVERHEAD;             \
         bl      hdlr;                                   \
         b       .ret_from_except_lite
@@ -407,7 +405,6 @@ __start_interrupts:
 _machine_check_pSeries:
         HMT_MEDIUM
         mtspr   SPRN_SPRG1,r13          /* save r13 */
-        RUNLATCH_ON(r13)
         EXCEPTION_PROLOG_PSERIES(PACA_EXMC, machine_check_common)
 
         . = 0x300
@@ -434,7 +431,6 @@ END_FTR_SECTION_IFCLR(CPU_FTR_SLB)
 data_access_slb_pSeries:
         HMT_MEDIUM
         mtspr   SPRN_SPRG1,r13
-        RUNLATCH_ON(r13)
         mfspr   r13,SPRN_SPRG3          /* get paca address into r13 */
         std     r3,PACA_EXSLB+EX_R3(r13)
         mfspr   r3,SPRN_DAR
@@ -460,7 +456,6 @@ data_access_slb_pSeries:
 instruction_access_slb_pSeries:
         HMT_MEDIUM
         mtspr   SPRN_SPRG1,r13
-        RUNLATCH_ON(r13)
         mfspr   r13,SPRN_SPRG3          /* get paca address into r13 */
         std     r3,PACA_EXSLB+EX_R3(r13)
         mfspr   r3,SPRN_SRR0            /* SRR0 is faulting address */
@@ -491,7 +486,6 @@ instruction_access_slb_pSeries:
         .globl  system_call_pSeries
 system_call_pSeries:
         HMT_MEDIUM
-        RUNLATCH_ON(r9)
         mr      r9,r13
         mfmsr   r10
         mfspr   r13,SPRN_SPRG3
@@ -575,7 +569,6 @@ slb_miss_user_pseries:
 system_reset_fwnmi:
         HMT_MEDIUM
         mtspr   SPRN_SPRG1,r13          /* save r13 */
-        RUNLATCH_ON(r13)
         EXCEPTION_PROLOG_PSERIES(PACA_EXGEN, system_reset_common)
 
         .globl machine_check_fwnmi
@@ -583,7 +576,6 @@ system_reset_fwnmi:
 machine_check_fwnmi:
         HMT_MEDIUM
         mtspr   SPRN_SPRG1,r13          /* save r13 */
-        RUNLATCH_ON(r13)
         EXCEPTION_PROLOG_PSERIES(PACA_EXMC, machine_check_common)
 
 #ifdef CONFIG_PPC_ISERIES
@@ -894,7 +886,6 @@ unrecov_fer:
         .align  7
         .globl data_access_common
 data_access_common:
-        RUNLATCH_ON(r10)                /* It wont fit in the 0x300 handler */
         mfspr   r10,SPRN_DAR
         std     r10,PACA_EXGEN+EX_DAR(r13)
         mfspr   r10,SPRN_DSISR
@@ -1042,6 +1033,7 @@ hardware_interrupt_common:
         EXCEPTION_PROLOG_COMMON(0x500, PACA_EXGEN)
 hardware_interrupt_entry:
         DISABLE_INTS
+        bl      .ppc64_runlatch_on
         addi    r3,r1,STACK_FRAME_OVERHEAD
         bl      .do_IRQ
         b       .ret_from_except_lite
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 57703994a063..c225cf154bfe 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -888,3 +888,35 @@ void dump_stack(void)
         show_stack(current, NULL);
 }
 EXPORT_SYMBOL(dump_stack);
+
+#ifdef CONFIG_PPC64
+void ppc64_runlatch_on(void)
+{
+        unsigned long ctrl;
+
+        if (cpu_has_feature(CPU_FTR_CTRL) && !test_thread_flag(TIF_RUNLATCH)) {
+                HMT_medium();
+
+                ctrl = mfspr(SPRN_CTRLF);
+                ctrl |= CTRL_RUNLATCH;
+                mtspr(SPRN_CTRLT, ctrl);
+
+                set_thread_flag(TIF_RUNLATCH);
+        }
+}
+
+void ppc64_runlatch_off(void)
+{
+        unsigned long ctrl;
+
+        if (cpu_has_feature(CPU_FTR_CTRL) && test_thread_flag(TIF_RUNLATCH)) {
+                HMT_medium();
+
+                clear_thread_flag(TIF_RUNLATCH);
+
+                ctrl = mfspr(SPRN_CTRLF);
+                ctrl &= ~CTRL_RUNLATCH;
+                mtspr(SPRN_CTRLT, ctrl);
+        }
+}
+#endif