From: Alexey Brodkin alexey.brodkin@synopsys.com
It turned out we used to use default implementation of sched_clock() from kernel/sched/clock.c which was as precise as 1/HZ, i.e. by default we had 10 msec granularity of time measurement.
Now given ARC built-in timers are clocked with the same frequency as CPU cores we may get much higher precision of time tracking.
Thus we switch to generic sched_clock which really reads ARC hardware counters.
This is especially helpful for measuring short events. That's what we used to have: ------------------------------>8------------------------ $ perf stat /bin/sh -c /root/lmbench-master/bin/arc/hello > /dev/null
Performance counter stats for '/bin/sh -c /root/lmbench-master/bin/arc/hello':
10.000000 task-clock (msec) # 2.832 CPUs utilized 1 context-switches # 0.100 K/sec 1 cpu-migrations # 0.100 K/sec 63 page-faults # 0.006 M/sec 3049480 cycles # 0.305 GHz 1091259 instructions # 0.36 insn per cycle 256828 branches # 25.683 M/sec 27026 branch-misses # 10.52% of all branches
0.003530687 seconds time elapsed
0.000000000 seconds user 0.010000000 seconds sys ------------------------------>8------------------------
And now we'll see: ------------------------------>8------------------------ $ perf stat /bin/sh -c /root/lmbench-master/bin/arc/hello > /dev/null
Performance counter stats for '/bin/sh -c /root/lmbench-master/bin/arc/hello':
3.004322 task-clock (msec) # 0.865 CPUs utilized 1 context-switches # 0.333 K/sec 1 cpu-migrations # 0.333 K/sec 63 page-faults # 0.021 M/sec 2986734 cycles # 0.994 GHz 1087466 instructions # 0.36 insn per cycle 255209 branches # 84.947 M/sec 26002 branch-misses # 10.19% of all branches
0.003474829 seconds time elapsed
0.003519000 seconds user 0.000000000 seconds sys ------------------------------>8------------------------
Note how much more meaningful is the second output - time spent for execution pretty much matches number of cycles spent (we're runnign @ 1GHz here).
Signed-off-by: Alexey Brodkin abrodkin@synopsys.com Cc: Daniel Lezcano daniel.lezcano@linaro.org Cc: Vineet Gupta vgupta@synopsys.com Cc: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Acked-by: Vineet Gupta vgupta@synopsys.com Signed-off-by: Daniel Lezcano daniel.lezcano@linaro.org
Signed-off-by: Daniel Lezcano daniel.lezcano@linaro.org --- arch/arc/Kconfig | 1 + drivers/clocksource/Kconfig | 1 + drivers/clocksource/arc_timer.c | 22 ++++++++++++++++++++++ 3 files changed, 24 insertions(+)
diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig index c9e2a1323536..74b5a654f664 100644 --- a/arch/arc/Kconfig +++ b/arch/arc/Kconfig @@ -26,6 +26,7 @@ config ARC select GENERIC_IRQ_SHOW select GENERIC_PCI_IOMAP select GENERIC_PENDING_IRQ if SMP + select GENERIC_SCHED_CLOCK select GENERIC_SMP_IDLE_THREAD select HAVE_ARCH_KGDB select HAVE_ARCH_TRACEHOOK diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig index 8761a1c21b6c..c57b156f49a2 100644 --- a/drivers/clocksource/Kconfig +++ b/drivers/clocksource/Kconfig @@ -277,6 +277,7 @@ config CLKSRC_MPS2
config ARC_TIMERS bool "Support for 32-bit TIMERn counters in ARC Cores" if COMPILE_TEST + depends on GENERIC_SCHED_CLOCK select TIMER_OF help These are legacy 32-bit TIMER0 and TIMER1 counters found on all ARC cores diff --git a/drivers/clocksource/arc_timer.c b/drivers/clocksource/arc_timer.c index 20da9b1d7f7d..b28970ca4a7a 100644 --- a/drivers/clocksource/arc_timer.c +++ b/drivers/clocksource/arc_timer.c @@ -23,6 +23,7 @@ #include <linux/cpu.h> #include <linux/of.h> #include <linux/of_irq.h> +#include <linux/sched_clock.h>
#include <soc/arc/timers.h> #include <soc/arc/mcip.h> @@ -88,6 +89,11 @@ static u64 arc_read_gfrc(struct clocksource *cs) return (((u64)h) << 32) | l; }
+static notrace u64 arc_gfrc_clock_read(void) +{ + return arc_read_gfrc(NULL); +} + static struct clocksource arc_counter_gfrc = { .name = "ARConnect GFRC", .rating = 400, @@ -111,6 +117,8 @@ static int __init arc_cs_setup_gfrc(struct device_node *node) if (ret) return ret;
+ sched_clock_register(arc_gfrc_clock_read, 64, arc_timer_freq); + return clocksource_register_hz(&arc_counter_gfrc, arc_timer_freq); } TIMER_OF_DECLARE(arc_gfrc, "snps,archs-timer-gfrc", arc_cs_setup_gfrc); @@ -139,6 +147,11 @@ static u64 arc_read_rtc(struct clocksource *cs) return (((u64)h) << 32) | l; }
+static notrace u64 arc_rtc_clock_read(void) +{ + return arc_read_rtc(NULL); +} + static struct clocksource arc_counter_rtc = { .name = "ARCv2 RTC", .rating = 350, @@ -170,6 +183,8 @@ static int __init arc_cs_setup_rtc(struct device_node *node)
write_aux_reg(AUX_RTC_CTRL, 1);
+ sched_clock_register(arc_rtc_clock_read, 64, arc_timer_freq); + return clocksource_register_hz(&arc_counter_rtc, arc_timer_freq); } TIMER_OF_DECLARE(arc_rtc, "snps,archs-timer-rtc", arc_cs_setup_rtc); @@ -185,6 +200,11 @@ static u64 arc_read_timer1(struct clocksource *cs) return (u64) read_aux_reg(ARC_REG_TIMER1_CNT); }
+static notrace u64 arc_timer1_clock_read(void) +{ + return arc_read_timer1(NULL); +} + static struct clocksource arc_counter_timer1 = { .name = "ARC Timer1", .rating = 300, @@ -209,6 +229,8 @@ static int __init arc_cs_setup_timer1(struct device_node *node) write_aux_reg(ARC_REG_TIMER1_CNT, 0); write_aux_reg(ARC_REG_TIMER1_CTRL, TIMER_CTRL_NH);
+ sched_clock_register(arc_timer1_clock_read, 32, arc_timer_freq); + return clocksource_register_hz(&arc_counter_timer1, arc_timer_freq); }