Hi Daniel, On Mon, 2018-11-19 at 22:50 +0100, Daniel Lezcano wrote: > On 19/11/2018 12:29, Alexey Brodkin wrote: > > 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 <abrod...@synopsys.com> > > Cc: Daniel Lezcano <daniel.lezc...@linaro.org> > > Cc: Vineet Gupta <vgu...@synopsys.com> > > Cc: Thomas Gleixner <t...@linutronix.de> > > --- > > Applied, thanks.
Maybe a bit too late but I completely forgot to add stable tag into Cc list. Any chance to add it still? -Alexey
