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| author | Alexey Brodkin <alexey.brodkin@synopsys.com> | 2018-11-19 14:29:17 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-01-09 17:38:42 +0100 |
| commit | bf75d9382bc4c57873c4193f90685058b6adf934 (patch) | |
| tree | 2a7caaccd922e84e5e86ebf5f97cd6ec37084915 /arch/arc | |
| parent | ca3a6fd272bb446a240b0b5c29980e1ac54aaa40 (diff) | |
| download | linux-stable-bf75d9382bc4c57873c4193f90685058b6adf934.tar.gz linux-stable-bf75d9382bc4c57873c4193f90685058b6adf934.tar.bz2 linux-stable-bf75d9382bc4c57873c4193f90685058b6adf934.zip | |
clocksource/drivers/arc_timer: Utilize generic sched_clock
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@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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/arc')
| -rw-r--r-- | arch/arc/Kconfig | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig index a90c4f126050..ac69f307dcfe 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 |