On 2014/5/28 4:53, Thomas Gleixner wrote: > On Tue, 27 May 2014, Libo Chen wrote: >> On 2014/5/27 17:55, Mike Galbraith wrote: >>> On Tue, 2014-05-27 at 15:56 +0800, Libo Chen wrote: >>>>> On 2014/5/26 22:19, Mike Galbraith wrote: >>>>>>> On Mon, 2014-05-26 at 20:16 +0800, Libo Chen wrote: >>>>>>>>> On 2014/5/26 13:11, Mike Galbraith wrote: >>>>>>> >>>>>>>>>>> Your synthetic test is the absolute worst case scenario. There has >>>>>>>>>>> to >>>>>>>>>>> be work between wakeups for select_idle_sibling() to have any chance >>>>>>>>>>> whatsoever of turning in a win. At 0 work, it becomes 100% >>>>>>>>>>> overhead. >>>>>>>>> >>>>>>>>> not synthetic, it is a real problem in our product. under no load, >>>>>>>>> waste >>>>>>>>> much cpu time. >>>>>>> >>>>>>> What happens in your product if you apply the commit I pointed out? >>>>> >>>>> under no load, cpu usage is up to 60%, but the same apps cost 10% on >>>>> susp sp1. The apps use a lot of timer. >>> Something is rotten. 3.14-rt contains that commit, I ran your test with >>> 256 threads on 64 core box, saw ~4%. >>> >>> Putting master/nopreempt config on box and doing the same test, box is >>> chewing up truckloads of CPU, but not from migrations. >>> >>> perf top -g --sort=symbol >> in my box: >> >> perf top -g --sort=symbol >> >> Events: 3K cycles >> 73.27% [k] read_hpet > > Why is that machine using read_hpet() ? > > Please provide the output of > > # dmesg | grep -i tsc >
Euler:/home # dmesg | grep -i tsc [ 0.000000] Fast TSC calibration using PIT [ 0.226921] TSC synchronization [CPU#0 -> CPU#1]: [ 0.227142] Measured 1053728 cycles TSC warp between CPUs, turning off TSC clock. [ 0.008000] Marking TSC unstable due to check_tsc_sync_source failed > and > > # cat /sys/devices/system/clocksource/clocksource0/available_clocksource hpet acpi_pm > > and > > # cat /sys/devices/system/clocksource/clocksource0/current_clocksource hpet > > Thanks, > > tglx > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > > . > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
