2013/4/4 Christoph Lameter <c...@linux.com>: > It seems that nohz still has no effect. > > 3.9-rc5 + patches. Affinity of init set to 0,1 so no > tasks are running on 9. The "latencytest" used here is part of my > lldiag-0.15 toolkit. > > First test without any special kernel parameters. nohz off right? > > $ nice -5 taskset -c 9 latencytest > > CPUs: Freq=2.90Ghz Processors=32 Cores=8 cacheline_size=64 Intel(R) > Xeon(R) CPU E5-2690 0 @ 2.90GHz > 16775106 samples below 1000 nsec > 13 involuntary context switches > 1019 (0.00607411%) variances in 10.00 seconds: minimum 1.07us maximum 12.32us > average 3.30us stddev 0.63us > > HZ=100 so the 1019 variances are likely timer interrupts. > > > > > After nohz setup > > /proc/cmdline: > > BOOT_IMAGE=/vmlinuz-3.9.0-rc5+ root=/dev/mapper/vg01-root ro console=tty0 > console=ttyS0,115200 idle=mwait rcu_nocb_poll rcu_nocbs=2-31 > nohz_extended=2-31 > > $ nice -5 taskset -c 9 latencytest > CPUs: Freq=2.90Ghz Processors=32 Cores=8 cacheline_size=64 Intel(R) > Xeon(R) CPU E5-2690 0 @ 2.90GHz > 16779362 samples below 1000 nsec > 13 involuntary context switches > 1037 (0.00617983%) variances in 10.00 seconds: minimum 1.00us maximum 10.61us > average 3.30us stddev 0.98us > > > > If I move the RCU threads off the cpu then I get a slightly better result: > > $ nice -5 taskset -c 9 latencytest > CPUs: Freq=2.90Ghz Processors=32 Cores=8 cacheline_size=64 Intel(R) > Xeon(R) CPU E5-2690 0 @ 2.90GHz > 16796039 samples below 1000 nsec > 12 involuntary context switches > 1020 (0.00607249%) variances in 10.00 seconds: minimum 1.00us maximum 11.58us > average 2.77us stddev 0.55us > > > > Why is the tick not stopping? How do I diagnose this? (I can start > patching the kernel again like last time but isnt there a better way?)
I don't know which tree you are using. But if you have that patch in: http://git.kernel.org/cgit/linux/kernel/git/frederic/linux-dynticks.git/commit/?h=3.9-rc1-nohz1&id=451128553e5e827dccc6cbcd24238470ec693d90 looking at the traces on that CPU may give you a few hints. Then you can dig deeper by looking at the sched_switch, timers, irq, ... events -- 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/
