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| author |   Alexey Brodkin <alexey.brodkin@synopsys.com> | 2018-11-19 14:29:17 +0300 |
|---|---|---|
| committer |   Daniel Lezcano <daniel.lezcano@linaro.org> | 2018-12-18 22:22:23 +0100 |
| commit | bf287607c80f24387fedb431a346dc67f25be12c (patch) | |
| tree | c2c0450742868addbf70642c01504c12e559048c /drivers/clocksource/Kconfig | |
| parent | dt-bindings: timer: renesas, cmt: Document r8a77470 CMT support (diff) | |
| download | linux-dev-bf287607c80f24387fedb431a346dc67f25be12c.tar.xz linux-dev-bf287607c80f24387fedb431a346dc67f25be12c.zip | |
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>
Diffstat (limited to 'drivers/clocksource/Kconfig')
| -rw-r--r-- | drivers/clocksource/Kconfig | 1 |
1 files changed, 1 insertions, 0 deletions
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 |