On Tue, 9 Jan 2018 15:42:35 -0200 Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx> wrote: > Em Mon, 8 Jan 2018 11:51:04 -0800 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> escreveu: > [...] > Patch makes sense to me, although I was not able to test it myself. The patch also make sense to me. I've done some basic testing with it on my high-end Broadwell system (that I use for 100Gbit/s testing). As expected the network overload case still works, as NET_RX_SOFTIRQ is not matched. > I set a RPi3 machine here with vanilla Kernel 4.14.11 running a > standard raspbian distribution (with elevator=deadline). I found a Raspberry Pi Model B+ (I think, BCM2835), that I loaded the LibreELEC distro on. One of the guys even created an image for me with a specific kernel[1] (that I just upgraded the system with). [1] https://forum.libreelec.tv/thread/4235-dvb-issue-since-le-switched-to-kernel-4-9-x/?postID=77031#post77031 > My plan is to do more tests along this week, and try to tweak a little > bit both userspace and kernelspace, in order to see if I can get > better results. 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. Thus, if you manage to reproduce the case, try to see if adjusting this can mitigate the issue... Their system have non-preempt kernel, should they use PREEMPT? LibreELEC:~ # uname -a Linux LibreELEC 4.14.10 #1 SMP Tue Jan 9 17:35:03 GMT 2018 armv7l GNU/Linux [2] https://forum.libreelec.tv/thread/4235-dvb-issue-since-le-switched-to-kernel-4-9-x/?postID=76999#post76999 -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
