On 01/13/2016 07:58 PM, Sebastian Andrzej Siewior wrote:
* Mike Galbraith | 2016-01-01 08:19:41 [+0100]:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
3 root -2 0 0 0 0 S 37.3 0.0 307:52.44 ksoftirqd/0
32 root -2 0 0 0 0 S 37.3 0.0 308:08.72 ksoftirqd/2
42 root -2 0 0 0 0 R 37.3 0.0 308:32.84 ksoftirqd/3
22 root -2 0 0 0 0 S 26.9 0.0 222:29.82 ksoftirqd/1
1 root 20 0 46628 6980 4976 S 1.3 0.2 0:13.98 systemd
22358 williams 20 0 159980 4552 3780 R 1.0 0.1 0:00.39 top
Heh, I didn't notice immediately because I throttle nohz, am seeing
only tiny utilization (but nohz idle isn't working). With throttle
patch removed, box is screaming, expires=4294990471 pokes eyeball.
This is due to NO_HZ as far as I can tell. My AMD A10 in idle mode has
0.7% utilisation of ksoftirqd/ with CONFIG_HZ_PERIODIC and with
CONFIG_NO_HZ_FULL it shows about 25% on all CPU threads.
I might be wrong completely, but could below two patches affect on
CPU utilization of ksoftirqd?
6047967 ksoftirqd: Use new cond_resched_rcu_qs() function
28423ad ksoftirqd: Enable IRQs and call cond_resched() before poking RCU
above two patches are not applied on -RT part of softirqs processing.
static void run_ksoftirqd(unsigned int cpu)
{
local_irq_disable();
current->softirq_nestcnt++;
do_current_softirqs();
current->softirq_nestcnt--;
rcu_note_context_switch();
^^^ IRQs disabled
local_irq_enable();
}
--
regards,
-grygorii
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