powerpc: tracing: Add hypervisor call tracepoints

Add hcall_entry and hcall_exit tracepoints.  This replaces the inline
assembly HCALL_STATS code and converts it to use the new tracepoints.

To keep the disabled case as quick as possible, we embed a status word
in the TOC so we can get at it with a single load.  By doing so we
keep the overhead at a minimum.  Time taken for a null hcall:

No tracepoint code:	135.79 cycles
Disabled tracepoints:	137.95 cycles

For reference, before this patch enabling HCALL_STATS resulted in a null
hcall of 201.44 cycles!

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

3 files changed, 127 insertions, 43 deletions

diff --git a/arch/powerpc/platforms/pseries/hvCall.S b/arch/powerpc/platforms/pseries/hvCall.S
index c1427b3634ec..01e95ab18d35 100644
--- a/arch/powerpc/platforms/pseries/hvCall.S
+++ b/arch/powerpc/platforms/pseries/hvCall.S
@@ -14,20 +14,54 @@
         
 #define STK_PARM(i)     (48 + ((i)-3)*8)
 
-#ifdef CONFIG_HCALL_STATS
+#ifdef CONFIG_TRACEPOINTS
+
+        .section        ".toc","aw"
+
+        .globl hcall_tracepoint_refcount
+hcall_tracepoint_refcount:
+        .llong  0
+
+        .section        ".text"
+
 /*
  * precall must preserve all registers.  use unused STK_PARM()
- * areas to save snapshots and opcode.
+ * areas to save snapshots and opcode. We branch around this
+ * in early init (eg when populating the MMU hashtable) by using an
+ * unconditional cpu feature.
  */
 #define HCALL_INST_PRECALL                                      \
-        std     r3,STK_PARM(r3)(r1);    /* save opcode */       \
-        mftb    r0;                     /* get timebase and */  \
-        std     r0,STK_PARM(r5)(r1);    /* save for later */    \
 BEGIN_FTR_SECTION;                                              \
-        mfspr   r0,SPRN_PURR;           /* get PURR and */      \
-        std     r0,STK_PARM(r6)(r1);    /* save for later */    \
-END_FTR_SECTION_IFSET(CPU_FTR_PURR);
-        
+        b       1f;                                             \
+END_FTR_SECTION(0, 1);                                          \
+        ld      r12,hcall_tracepoint_refcount@toc(r2);          \
+        cmpdi   r12,0;                                          \
+        beq+    1f;                                             \
+        mflr    r0;                                             \
+        std     r3,STK_PARM(r3)(r1);                            \
+        std     r4,STK_PARM(r4)(r1);                            \
+        std     r5,STK_PARM(r5)(r1);                            \
+        std     r6,STK_PARM(r6)(r1);                            \
+        std     r7,STK_PARM(r7)(r1);                            \
+        std     r8,STK_PARM(r8)(r1);                            \
+        std     r9,STK_PARM(r9)(r1);                            \
+        std     r10,STK_PARM(r10)(r1);                          \
+        std     r0,16(r1);                                      \
+        stdu    r1,-STACK_FRAME_OVERHEAD(r1);                   \
+        bl      .__trace_hcall_entry;                           \
+        addi    r1,r1,STACK_FRAME_OVERHEAD;                     \
+        ld      r0,16(r1);                                      \
+        ld      r3,STK_PARM(r3)(r1);                            \
+        ld      r4,STK_PARM(r4)(r1);                            \
+        ld      r5,STK_PARM(r5)(r1);                            \
+        ld      r6,STK_PARM(r6)(r1);                            \
+        ld      r7,STK_PARM(r7)(r1);                            \
+        ld      r8,STK_PARM(r8)(r1);                            \
+        ld      r9,STK_PARM(r9)(r1);                            \
+        ld      r10,STK_PARM(r10)(r1);                          \
+        mtlr    r0;                                             \
+1:
+
 /*
  * postcall is performed immediately before function return which
  * allows liberal use of volatile registers.  We branch around this
@@ -38,40 +72,21 @@ END_FTR_SECTION_IFSET(CPU_FTR_PURR);
 BEGIN_FTR_SECTION;                                              \
         b       1f;                                             \
 END_FTR_SECTION(0, 1);                                          \
-        ld      r4,STK_PARM(r3)(r1);    /* validate opcode */   \
-        cmpldi  cr7,r4,MAX_HCALL_OPCODE;                        \
-        bgt-    cr7,1f;                                         \
-                                                                \
-        /* get time and PURR snapshots after hcall */           \
-        mftb    r7;                     /* timebase after */    \
-BEGIN_FTR_SECTION;                                              \
-        mfspr   r8,SPRN_PURR;           /* PURR after */        \
-        ld      r6,STK_PARM(r6)(r1);    /* PURR before */       \
-        subf    r6,r6,r8;               /* delta */             \
-END_FTR_SECTION_IFSET(CPU_FTR_PURR);                            \
-        ld      r5,STK_PARM(r5)(r1);    /* timebase before */   \
-        subf    r5,r5,r7;               /* time delta */        \
-                                                                \
-        /* calculate address of stat structure r4 = opcode */   \
-        srdi    r4,r4,2;                /* index into array */  \
-        mulli   r4,r4,HCALL_STAT_SIZE;                          \
-        LOAD_REG_ADDR(r7, per_cpu__hcall_stats);                \
-        add     r4,r4,r7;                                       \
-        ld      r7,PACA_DATA_OFFSET(r13); /* per cpu offset */  \
-        add     r4,r4,r7;                                       \
-                                                                \
-        /* update stats */                                      \
-        ld      r7,HCALL_STAT_CALLS(r4); /* count */            \
-        addi    r7,r7,1;                                        \
-        std     r7,HCALL_STAT_CALLS(r4);                        \
-        ld      r7,HCALL_STAT_TB(r4);   /* timebase */          \
-        add     r7,r7,r5;                                       \
-        std     r7,HCALL_STAT_TB(r4);                           \
-BEGIN_FTR_SECTION;                                              \
-        ld      r7,HCALL_STAT_PURR(r4); /* PURR */              \
-        add     r7,r7,r6;                                       \
-        std     r7,HCALL_STAT_PURR(r4);                         \
-END_FTR_SECTION_IFSET(CPU_FTR_PURR);                            \
+        ld      r12,hcall_tracepoint_refcount@toc(r2);          \
+        cmpdi   r12,0;                                          \
+        beq+    1f;                                             \
+        mflr    r0;                                             \
+        ld      r6,STK_PARM(r3)(r1);                            \
+        std     r3,STK_PARM(r3)(r1);                            \
+        mr      r4,r3;                                          \
+        mr      r3,r6;                                          \
+        std     r0,16(r1);                                      \
+        stdu    r1,-STACK_FRAME_OVERHEAD(r1);                   \
+        bl      .__trace_hcall_exit;                            \
+        addi    r1,r1,STACK_FRAME_OVERHEAD;                     \
+        ld      r0,16(r1);                                      \
+        ld      r3,STK_PARM(r3)(r1);                            \
+        mtlr    r0;                                             \
 1:
 #else
 #define HCALL_INST_PRECALL
diff --git a/arch/powerpc/platforms/pseries/hvCall_inst.c b/arch/powerpc/platforms/pseries/hvCall_inst.c
index 3631a4f277eb..e44e1035f133 100644
--- a/arch/powerpc/platforms/pseries/hvCall_inst.c
+++ b/arch/powerpc/platforms/pseries/hvCall_inst.c
@@ -26,6 +26,7 @@
 #include <asm/hvcall.h>
 #include <asm/firmware.h>
 #include <asm/cputable.h>
+#include <asm/trace.h>
 
 DEFINE_PER_CPU(struct hcall_stats[HCALL_STAT_ARRAY_SIZE], hcall_stats);
 
@@ -100,6 +101,34 @@ static const struct file_operations hcall_inst_seq_fops = {
 #define HCALL_ROOT_DIR          "hcall_inst"
 #define CPU_NAME_BUF_SIZE       32
 
+
+static void probe_hcall_entry(unsigned long opcode)
+{
+        struct hcall_stats *h;
+
+        if (opcode > MAX_HCALL_OPCODE)
+                return;
+
+        h = &get_cpu_var(hcall_stats)[opcode / 4];
+        h->tb_start = mftb();
+        h->purr_start = mfspr(SPRN_PURR);
+}
+
+static void probe_hcall_exit(unsigned long opcode, unsigned long retval)
+{
+        struct hcall_stats *h;
+
+        if (opcode > MAX_HCALL_OPCODE)
+                return;
+
+        h = &__get_cpu_var(hcall_stats)[opcode / 4];
+        h->num_calls++;
+        h->tb_total = mftb() - h->tb_start;
+        h->purr_total = mfspr(SPRN_PURR) - h->purr_start;
+
+        put_cpu_var(hcall_stats);
+}
+
 static int __init hcall_inst_init(void)
 {
         struct dentry *hcall_root;
@@ -110,6 +139,14 @@ static int __init hcall_inst_init(void)
         if (!firmware_has_feature(FW_FEATURE_LPAR))
                 return 0;
 
+        if (register_trace_hcall_entry(probe_hcall_entry))
+                return -EINVAL;
+
+        if (register_trace_hcall_exit(probe_hcall_exit)) {
+                unregister_trace_hcall_entry(probe_hcall_entry);
+                return -EINVAL;
+        }
+
         hcall_root = debugfs_create_dir(HCALL_ROOT_DIR, NULL);
         if (!hcall_root)
                 return -ENOMEM;
diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 903eb9eec687..4b7b6e8e32de 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -39,6 +39,7 @@
 #include <asm/cputable.h>
 #include <asm/udbg.h>
 #include <asm/smp.h>
+#include <asm/trace.h>
 
 #include "plpar_wrappers.h"
 #include "pseries.h"
@@ -661,3 +662,34 @@ void arch_free_page(struct page *page, int order)
 EXPORT_SYMBOL(arch_free_page);
 
 #endif
+
+#ifdef CONFIG_TRACEPOINTS
+/*
+ * We optimise our hcall path by placing hcall_tracepoint_refcount
+ * directly in the TOC so we can check if the hcall tracepoints are
+ * enabled via a single load.
+ */
+
+/* NB: reg/unreg are called while guarded with the tracepoints_mutex */
+extern long hcall_tracepoint_refcount;
+
+void hcall_tracepoint_regfunc(void)
+{
+        hcall_tracepoint_refcount++;
+}
+
+void hcall_tracepoint_unregfunc(void)
+{
+        hcall_tracepoint_refcount--;
+}
+
+void __trace_hcall_entry(unsigned long opcode)
+{
+        trace_hcall_entry(opcode);
+}
+
+void __trace_hcall_exit(long opcode, unsigned long retval)
+{
+        trace_hcall_exit(opcode, retval);
+}
+#endif