powerpc: Account time using timebase rather than PURR

Currently, when CONFIG_VIRT_CPU_ACCOUNTING is enabled, we use the
PURR register for measuring the user and system time used by
processes, as well as other related times such as hardirq and
softirq times.  This turns out to be quite confusing for users
because it means that a program will often be measured as taking
less time when run on a multi-threaded processor (SMT2 or SMT4 mode)
than it does when run on a single-threaded processor (ST mode), even
though the program takes longer to finish.  The discrepancy is
accounted for as stolen time, which is also confusing, particularly
when there are no other partitions running.

This changes the accounting to use the timebase instead, meaning that
the reported user and system times are the actual number of real-time
seconds that the program was executing on the processor thread,
regardless of which SMT mode the processor is in.  Thus a program will
generally show greater user and system times when run on a
multi-threaded processor than on a single-threaded processor.

On pSeries systems on POWER5 or later processors, we measure the
stolen time (time when this partition wasn't running) using the
hypervisor dispatch trace log.  We check for new entries in the
log on every entry from user mode and on every transition from
kernel process context to soft or hard IRQ context (i.e. when
account_system_vtime() gets called).  So that we can correctly
distinguish time stolen from user time and time stolen from system
time, without having to check the log on every exit to user mode,
we store separate timestamps for exit to user mode and entry from
user mode.

On systems that have a SPURR (POWER6 and POWER7), we read the SPURR
in account_system_vtime() (as before), and then apportion the SPURR
ticks since the last time we read it between scaled user time and
scaled system time according to the relative proportions of user
time and system time over the same interval.  This avoids having to
read the SPURR on every kernel entry and exit.  On systems that have
PURR but not SPURR (i.e., POWER5), we do the same using the PURR
rather than the SPURR.

This disables the DTL user interface in /sys/debug/kernel/powerpc/dtl
for now since it conflicts with the use of the dispatch trace log
by the time accounting code.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 31 insertions, 19 deletions

diff --git a/arch/powerpc/include/asm/ppc_asm.h b/arch/powerpc/include/asm/ppc_asm.h
index 498fe09263d3..98210067c1cc 100644
--- a/arch/powerpc/include/asm/ppc_asm.h
+++ b/arch/powerpc/include/asm/ppc_asm.h
@@ -9,6 +9,7 @@
 #include <asm/asm-compat.h>
 #include <asm/processor.h>
 #include <asm/ppc-opcode.h>
+#include <asm/firmware.h>
 
 #ifndef __ASSEMBLY__
 #error __FILE__ should only be used in assembler files
@@ -26,17 +27,13 @@
 #ifndef CONFIG_VIRT_CPU_ACCOUNTING
 #define ACCOUNT_CPU_USER_ENTRY(ra, rb)
 #define ACCOUNT_CPU_USER_EXIT(ra, rb)
+#define ACCOUNT_STOLEN_TIME
 #else
 #define ACCOUNT_CPU_USER_ENTRY(ra, rb)					\
 	beq	2f;			/* if from kernel mode */	\
-BEGIN_FTR_SECTION;							\
-	mfspr	ra,SPRN_PURR;		/* get processor util. reg */	\
-END_FTR_SECTION_IFSET(CPU_FTR_PURR);					\
-BEGIN_FTR_SECTION;							\
-	MFTB(ra);			/* or get TB if no PURR */	\
-END_FTR_SECTION_IFCLR(CPU_FTR_PURR);					\
-	ld	rb,PACA_STARTPURR(r13);					\
-	std	ra,PACA_STARTPURR(r13);					\
+	MFTB(ra);			/* get timebase */		\
+	ld	rb,PACA_STARTTIME_USER(r13);				\
+	std	ra,PACA_STARTTIME(r13);					\
 	subf	rb,rb,ra;		/* subtract start value */	\
 	ld	ra,PACA_USER_TIME(r13);					\
 	add	ra,ra,rb;		/* add on to user time */	\
@@ -44,19 +41,34 @@ END_FTR_SECTION_IFCLR(CPU_FTR_PURR);					\
 2:
 
 #define ACCOUNT_CPU_USER_EXIT(ra, rb)					\
-BEGIN_FTR_SECTION;							\
-	mfspr	ra,SPRN_PURR;		/* get processor util. reg */	\
-END_FTR_SECTION_IFSET(CPU_FTR_PURR);					\
-BEGIN_FTR_SECTION;							\
-	MFTB(ra);			/* or get TB if no PURR */	\
-END_FTR_SECTION_IFCLR(CPU_FTR_PURR);					\
-	ld	rb,PACA_STARTPURR(r13);					\
-	std	ra,PACA_STARTPURR(r13);					\
+	MFTB(ra);			/* get timebase */		\
+	ld	rb,PACA_STARTTIME(r13);					\
+	std	ra,PACA_STARTTIME_USER(r13);				\
 	subf	rb,rb,ra;		/* subtract start value */	\
 	ld	ra,PACA_SYSTEM_TIME(r13);				\
-	add	ra,ra,rb;		/* add on to user time */	\
-	std	ra,PACA_SYSTEM_TIME(r13);
-#endif
+	add	ra,ra,rb;		/* add on to system time */	\
+	std	ra,PACA_SYSTEM_TIME(r13)
+
+#ifdef CONFIG_PPC_SPLPAR
+#define ACCOUNT_STOLEN_TIME						\
+BEGIN_FW_FTR_SECTION;							\
+	beq	33f;							\
+	/* from user - see if there are any DTL entries to process */	\
+	ld	r10,PACALPPACAPTR(r13);	/* get ptr to VPA */		\
+	ld	r11,PACA_DTL_RIDX(r13);	/* get log read index */	\
+	ld	r10,LPPACA_DTLIDX(r10);	/* get log write index */	\
+	cmpd	cr1,r11,r10;						\
+	beq+	cr1,33f;						\
+	bl	.accumulate_stolen_time;				\
+33:									\
+END_FW_FTR_SECTION_IFSET(FW_FEATURE_SPLPAR)
+
+#else  /* CONFIG_PPC_SPLPAR */
+#define ACCOUNT_STOLEN_TIME
+
+#endif /* CONFIG_PPC_SPLPAR */
+
+#endif /* CONFIG_VIRT_CPU_ACCOUNTING */
 
 /*
  * Macros for storing registers into and loading registers from