clocksource/drivers/arc_timer: Utilize generic sched_clock
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>
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@ -26,6 +26,7 @@ config ARC
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select GENERIC_IRQ_SHOW
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select GENERIC_PCI_IOMAP
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select GENERIC_PENDING_IRQ if SMP
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select GENERIC_SCHED_CLOCK
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select GENERIC_SMP_IDLE_THREAD
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select HAVE_ARCH_KGDB
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select HAVE_ARCH_TRACEHOOK
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@ -277,6 +277,7 @@ config CLKSRC_MPS2
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config ARC_TIMERS
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bool "Support for 32-bit TIMERn counters in ARC Cores" if COMPILE_TEST
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depends on GENERIC_SCHED_CLOCK
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select TIMER_OF
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help
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These are legacy 32-bit TIMER0 and TIMER1 counters found on all ARC cores
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@ -23,6 +23,7 @@
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#include <linux/cpu.h>
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#include <linux/of.h>
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#include <linux/of_irq.h>
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#include <linux/sched_clock.h>
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#include <soc/arc/timers.h>
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#include <soc/arc/mcip.h>
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@ -88,6 +89,11 @@ static u64 arc_read_gfrc(struct clocksource *cs)
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return (((u64)h) << 32) | l;
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}
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static notrace u64 arc_gfrc_clock_read(void)
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{
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return arc_read_gfrc(NULL);
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}
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static struct clocksource arc_counter_gfrc = {
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.name = "ARConnect GFRC",
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.rating = 400,
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@ -111,6 +117,8 @@ static int __init arc_cs_setup_gfrc(struct device_node *node)
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if (ret)
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return ret;
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sched_clock_register(arc_gfrc_clock_read, 64, arc_timer_freq);
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return clocksource_register_hz(&arc_counter_gfrc, arc_timer_freq);
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}
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TIMER_OF_DECLARE(arc_gfrc, "snps,archs-timer-gfrc", arc_cs_setup_gfrc);
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@ -139,6 +147,11 @@ static u64 arc_read_rtc(struct clocksource *cs)
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return (((u64)h) << 32) | l;
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}
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static notrace u64 arc_rtc_clock_read(void)
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{
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return arc_read_rtc(NULL);
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}
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static struct clocksource arc_counter_rtc = {
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.name = "ARCv2 RTC",
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.rating = 350,
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@ -170,6 +183,8 @@ static int __init arc_cs_setup_rtc(struct device_node *node)
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write_aux_reg(AUX_RTC_CTRL, 1);
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sched_clock_register(arc_rtc_clock_read, 64, arc_timer_freq);
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return clocksource_register_hz(&arc_counter_rtc, arc_timer_freq);
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}
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TIMER_OF_DECLARE(arc_rtc, "snps,archs-timer-rtc", arc_cs_setup_rtc);
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@ -185,6 +200,11 @@ static u64 arc_read_timer1(struct clocksource *cs)
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return (u64) read_aux_reg(ARC_REG_TIMER1_CNT);
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}
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static notrace u64 arc_timer1_clock_read(void)
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{
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return arc_read_timer1(NULL);
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}
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static struct clocksource arc_counter_timer1 = {
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.name = "ARC Timer1",
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.rating = 300,
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@ -209,6 +229,8 @@ static int __init arc_cs_setup_timer1(struct device_node *node)
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write_aux_reg(ARC_REG_TIMER1_CNT, 0);
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write_aux_reg(ARC_REG_TIMER1_CTRL, TIMER_CTRL_NH);
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sched_clock_register(arc_timer1_clock_read, 32, arc_timer_freq);
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return clocksource_register_hz(&arc_counter_timer1, arc_timer_freq);
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}
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