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Message-Id: <20190107104445.551185789@linuxfoundation.org>
Date: Mon, 7 Jan 2019 13:31:40 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Alexey Brodkin <abrodkin@...opsys.com>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Vineet Gupta <vgupta@...opsys.com>,
Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 4.20 063/145] clocksource/drivers/arc_timer: Utilize generic sched_clock
4.20-stable review patch. If anyone has any objections, please let me know.
------------------
From: Alexey Brodkin <alexey.brodkin@...opsys.com>
commit bf287607c80f24387fedb431a346dc67f25be12c upstream.
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@...opsys.com>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: Vineet Gupta <vgupta@...opsys.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: stable@...r.kernel.org
Acked-by: Vineet Gupta <vgupta@...opsys.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
arch/arc/Kconfig | 1 +
drivers/clocksource/Kconfig | 1 +
drivers/clocksource/arc_timer.c | 22 ++++++++++++++++++++++
3 files changed, 24 insertions(+)
--- 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
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -290,6 +290,7 @@ 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
--- 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 clocksou
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(stru
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 clocksour
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(struc
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 clocks
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(st
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);
}
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