On 11/19/18 3:30 AM, 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 <abrodkin at synopsys.com> > Cc: Daniel Lezcano <daniel.lezcano at linaro.org> > Cc: Vineet Gupta <vgupta at synopsys.com> > Cc: Thomas Gleixner <tglx at linutronix.de> Acked-by: Vineet Gupta <vgupta at synopsys.com> Thx, -Vineet
