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authorAlexey Brodkin <alexey.brodkin@synopsys.com>2018-11-19 14:29:17 +0300
committerDaniel Lezcano <daniel.lezcano@linaro.org>2018-12-18 22:22:23 +0100
commitbf287607c80f24387fedb431a346dc67f25be12c (patch)
treec2c0450742868addbf70642c01504c12e559048c /arch/arc
parent2bbaf54216448486def1153486778a975a73041d (diff)
downloadlinux-bf287607c80f24387fedb431a346dc67f25be12c.tar.gz
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 'arch/arc')
-rw-r--r--arch/arc/Kconfig1
1 files changed, 1 insertions, 0 deletions
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