On Sat, 6 Jan 2018, Mauro Carvalho Chehab wrote:

Hi Josef,

Em Sat, 6 Jan 2018 16:04:16 +0100
"Josef Griebichler" [off-list ref] escreveu:

quoted

Hi,

the causing commit has been identified.
After reverting commit https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4cd13c21b207e80ddb1144c576500098f2d5f882
its working again.

Just replying to me won't magically fix this. The ones that were involved on
this patch should also be c/c, plus USB people. Just added them.

quoted

Please have a look into the thread https://forum.libreelec.tv/thread/4235-dvb-issue-since-le-switched-to-kernel-4-9-x/?pageNo=13
here are several users aknowledging the revert solves their issues with usb dvb cards.

I read the entire (long) thread there. In order to make easier for the
others, from what I understand, the problem happens on both x86 and arm,
although almost all comments there are mentioning tests with raspbian
Kernel (with uses a different USB host driver than the upstream one).

It happens when watching digital TV DVB-C channels, with usually means
a sustained bit rate of 11 MBps to 54 MBps.

The reports mention the dvbsky, with uses USB URB bulk transfers.
On every several minutes (5 to 10 mins), the stream suffer "glitches"
caused by frame losses.

The part of the thread that contains the bisect is at:
	https://forum.libreelec.tv/thread/4235-dvb-issue-since-le-switched-to-kernel-4-9-x/?postID=75965#post75965

It indirectly mentions another comment on the thread with points
to:
	https://github.com/raspberrypi/linux/issues/2134

There, it says that this fix part of the issues:
	https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=34f41c0316ed52b0b44542491d89278efdaa70e4

but it affects URB packet losses on a lesser extend.

The main issue is really the logic changes a the core softirq logic.

Using Kernel 4.14.10 on a Raspberry Pi 3 with 4cd13c2 commit reverted
fixed the issue. 

Joseph, is the above right? Anything else to mention? Does the
same issue affect also on x86 with vanilla Kernel 4.14.10?

-

It seems that the original patch were designed to solve some IRQ issues
with network cards with causes data losses on high traffic. However,
it is also causing bad effects on sustained high bandwidth demands
required by DVB cards, at least on some USB host drivers.

Alan/Greg/Eric/David:

Any ideas about how to fix it without causing regressions to
network?

It would be good to know what hardware was involved on the x86 system
and to have some timing data.  Can we see the output from lsusb and
usbmon, running on a vanilla kernel that gets plenty of video glitches?

Overall, this may be a very difficult problem to solve.  The
4cd13c21b207 commit was intended to improve throughput at the cost of
increased latency.  But then what do you do when the latency becomes
too high for the video subsystem to handle?

Alan Stern