On 24/10/2018 00:33, Vineet Gupta wrote: > On 10/17/2018 04:30 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 running >> @ 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> > > @Daniel is this going via timer tree or you want me to pick it up. I will take care of it. -- Daniel -- <http://www.linaro.org/> Linaro.org ? Open source software for ARM SoCs Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | <http://twitter.com/#!/linaroorg> Twitter | <http://www.linaro.org/linaro-blog/> Blog
