On 19/11/2018 10:31, Alexey Brodkin wrote: > Hi Daniel, > > On Sun, 2018-11-18 at 03:17 +0100, Daniel Lezcano wrote: >> On 05/11/2018 15:39, Daniel Lezcano wrote: >>> 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. >> >> Please resend without the arch Kconfig change > > I'm wondering if there's a problem with arc/arc/Kconfig change going > through your tree? This way it will be really atomic change and it will be > much easier to back-port (and that's what we'd really like to happen). > > If Vineet is OK with that IMHO it's safe to keep it in the one and only commit. > > Otherwise should I just split this patch in 2 and still submit them as series or > have 2 completely not-related patches one for you and one for Vineet? > > In that case do I understand correctly that we may enable GENERIC_SCHED_CLOCK > for ARC even before proposed change for arc_timer.c gets merged - i.e. with no > special GENERIC_SCHED_CLOCK driver we'll safely fall-back to jiffie-based > sched clock which we anyways use now when GENERIC_SCHED_CLOCK is disabled, right? The ARC's Kconfig part does not apply on tip/timers/core. As you described, sending a separate arc timer change is fine IMO. -- <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
