lkml.org 
[lkml]   [2018]   [Jan]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: dvb usb issues since kernel 4.9
From
Date
On Tue, 2018-01-09 at 22:26 +0100, Jesper Dangaard Brouer wrote:
>
> I've previously experienced that you can be affected by the scheduler
> granularity, which is adjustable (with CONFIG_SCHED_DEBUG=y):
>
> $ grep -H . /proc/sys/kernel/sched_*_granularity_ns
> /proc/sys/kernel/sched_min_granularity_ns:2250000
> /proc/sys/kernel/sched_wakeup_granularity_ns:3000000
>
> The above numbers were confirmed on the RPi2 (see[2]). With commit
> 4cd13c21b207 ("softirq: Let ksoftirqd do its job"), I expect/assume that
> softirq processing latency is bounded by the sched_wakeup_granularity_ns,
> which with 3 ms is not good enough for their use-case.

Note of caution wrt twiddling sched_wakeup_granularity_ns: it must
remain < sched_latency_ns/2 else you effectively disable wakeup
preemption completely, turning CFS into a tick granularity scheduler.

-Mike

\
 
 \ /
  Last update: 2018-01-14 23:20    [W:0.054 / U:0.412 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site