Tvheadend

Dear all, here is one more thread about the infamous continuity counter errors, and how I solved it.

First of all, my setup:
- Pentium G3440T, 32 GB ram, asrock Z97 Extreme6
- 4x low cost DVB-T usb receivers (Logilink VG0002A - identified as 1d19:1101 Dexatek Technology Ltd. DK DVB-T Dongle)
- Ubuntu 16.04.1 LTS - x86_64
- + a lot of services (samba, nfs server, backuppc, dropbox (client), apache, mysql, zabbix, grafana, ...)
- root fs : ext4, raid1 of 2 sata ssd (Samsung SSD 850 EVO 120GB)
- data : ext4, raid10 of 4 sata (WDC WD20EFRX 2TB)

I used mythtv years ago, so a decided to re-install mythtv, and I get continuity errors.

Then I tried tvheadend, still continuity errors...

Here is what I tried:
- disable USB power (usbcore.autosuspend)
- renice tvheadhend to 20
disabling all other services (I found that atop runs with nice 20!)
disabling cpu powersave (scaling governor)
- probably a lot of other things

Still continuity errors, but as shown in syslog, almost all continuity errors was every five minutes,
five minutes... five minutes is the setting I've set in dirty_writeback_centisecs (=30000).

So setting /proc/sys/vm/dirty_writeback_centisecs back to the default 500 fixed the continuity errors.

Since that setting appears nowhere in the forum, I decided to share it!

Best regards