mjhjmtu

I've been running Linux Mint with Cinnamon as my main operating system for a few years now, since version 17 (point something). Relatively recently, I'm getting annoying repeated short UI pauses. Pauses can range from barely perceptable to several seconds. Intervals vary a lot, but can be every several seconds. Right now, I'm getting delays of around two to three seconds every five to ten seconds. I've tried a few obvious things to fix it, but even when it seems to go away it just comes back again, so I don't think I'll fix this until I track down the cause, which is outside my skillset.

During the pauses, the mouse cursor still moves but everything else on screen stops - if I'm dragging a window around for example, it stays behind while the cursor carries on until the pause is over (dragging a terminal window around is my main how-much-is-this-happening-ATM test). Video stops, but the audio carries on. Everything suggests that everything is still working during the pause except the screen updates.

System is a bit old and not high-spec - AMD FX6300 Black Edition CPU, ASUS M5A97 R2.0 motherboard, 32GB RAM, Zotac GeForce GTX 650 graphics (using the nVidia driver), main drive is a SanDisk 480GB SSD. For unrelated reasons (annoying noise + heatwave) it has been cleared out, CPU cooler replaced, case fans replaced and everything cleared out thoroughly (third time for dust clearing this year IIRC) in the last few days. Symptoms predate this by a long while, and are continuing.

Things I've tried...

• Back in 18.3, rebooting to different kernel versions - rebooting itself reduces the problem for a while (from minutes to maybe an hour or so) but I couldn't identify any clear effect from that.


• Wiping the OS completely, deleting the partitions, and cleanly reinstalling with Linux Mint 19 - not really paranoia as I intended to do a clean install this time around anyway. Seemed to stop it for a day or so, but I wasn't doing normal things then anyway as I was still getting things set up again.


• ublock origin and noscript in Firefox, blocking everything I can with very few exceptions. Symptoms definitely aren't restricted to when Firefox is running, but it does seem to trigger more frequent and longer delays (or is it that I'm just that the longer since boot the more likely I am to have gone online?).


• 
  nethogs -v 1 and some other things to try and monitor in real time. The pauses might be associated with high CPU for the Cinnamon process. In 18.3 I was half-convinced Cinnamon was taking one core to 100%, and I just wasn't quite seeing that in System Monitor because the screen wasn't updating at the time - in 19, Cinnamon has bumps in CPU up to a few percent when it doesn't seem to be doing much (particularly no more than when it was showing 0% a few seconds earlier), but I don't see any sign that's associated with the pauses, and TBH nothing that would worry me if I wasn't looking for something to blame.


• 
  /var/log - I looked in logs including boot.log (using dmesg -F - it's basically telling me that the SSD is clean over and over), kern.log (hmmm but not sure), syslog (same), and Xorg.0.log (I'm not confident, but this looks fine as far as I can tell).


• Uninstalled some packages I don't need just in case, uninstalled a dubious Cinnamon desktop applet (Custom Application Menu I think) that I got warnings about after installing 19.

On the logs, the kern.log and syslog worry is messages similar to...

 Aug 5 06:28:47 steve-desktop kernel: [ 7429.750372] [UFW BLOCK] IN=enp2s0 OUT= MAC=<redacted> SRC=192.168.0.1 DST=224.0.0.1 LEN=32 TOS=0x00 PREC=0x00 TTL=1 ID=0 PROTO=2 
 Aug 5 06:30:53 steve-desktop kernel: [ 7555.753424] [UFW BLOCK] IN=enp2s0 OUT= MAC=<redacted> SRC=192.168.0.1 DST=224.0.0.1 LEN=28 TOS=0x00 PREC=0x00 TTL=1 ID=0 PROTO=2 
 Aug 5 06:30:53 steve-desktop kernel: [ 7555.753760] [UFW BLOCK] IN=enp2s0 OUT= MAC=<redacted> SRC=192.168.0.1 DST=224.0.0.1 LEN=32 TOS=0x00 PREC=0x00 TTL=1 ID=0 PROTO=2 
 Aug 5 06:32:59 steve-desktop kernel: [ 7681.756730] [UFW BLOCK] IN=enp2s0 OUT= MAC=<redacted> SRC=192.168.0.1 DST=224.0.0.1 LEN=28 TOS=0x00 PREC=0x00 TTL=1 ID=0 PROTO=2 
 Aug 5 06:32:59 steve-desktop kernel: [ 7681.757093] [UFW BLOCK] IN=enp2s0 OUT= MAC=<redacted> SRC=192.168.0.1 DST=224.0.0.1 LEN=32 TOS=0x00 PREC=0x00 TTL=1 ID=0 PROTO=2 

I think this is my router "broadcasting" something and maybe "UFW BLOCK" means the firewall is rejecting it? MAC redacted because I assume (not checked) that's my hardware and maybe not the best thing to include here. The rate of these is about right for the pauses just now, but I've had pauses, immediately checked the log, and not seen a new message. Then again, maybe it's still in a queue at that point.

The strongest reason I have to believe my router hasn't been compromised is that I power it off most of the time - I know that doesn't mean that much, and I have had the same (ISP supplied) router for some years now.

So - what's my next step?

EDIT - I forgot to include that I've run a full scan with clamav - apparently eBay and PayPal e-mail address spoofing happens a lot, even for some clearly genuine messages (but not important and never replied to), but no sign of malware on the system (at least not Linux malware - apparently AutoIt had a trojan in the examples which I've never looked at in my network-drivers-all-permanently-disabled Windows 7 partition).

EDIT - have now also tried switching to the open source Nouveau driver (pretty desperate - might have made sense for full crashes/lockups but probably not short pauses). A while after rebooting I'm still getting the pauses.

EDIT - installed and switched to xfce - full reboot, chose xfce at login (Cinnamon is still the default). So far no pauses, but it's only a few minutes. If I have to switch, it at least seems pretty painless - differences seem unimportant so far.

EDIT - OK, since logging in with xfce (well over an hour now), I had one delay that I noticed, though it was about 5 seconds. I'm tempted to dismiss that as probably unrelated, at least until I see a repeat.