Cinnamon desktop lagging, spiking CPU every other second

Lately my Cinnamon desktop environment (running on Linux Mint 18.2) has been a bit... laggy. Mouse movement is 100% fine; however every scrolling, window-moving, highlighting, video playing (as it seems to me, things that update window content) causes 100% CPU spikes on one core for half a second, repeating with 1-2 sec period, freezing whatever I was doing. Disk usage stays low during it. This also causes videos to desynchronize with their sound. Needless to say, it's extremely annoying. Between the lags it works as it should. My computer should handle Cinnamon well - Linux is installed on an SSD (though some directories, like ~HOME, are on an HDD), I have 4GB RAM and an i5 3.2gHz CPU, and running from a Raedon 5770 GPU (built-in driver). My inxi tells: ezio@Cantabury ~/Downloads $ inxi -F System: Host: Cantabury Kernel: 4.10.0-32-generic x86_64 (64 bit) Desktop: Cinnamon 3.4.6 Distro: Linux Mint 18.2 Sonya Machine: Mobo: ASRock model: H87M Pro4 Bios: American Megatrends v: P2.00 date: 12/06/2013 CPU: Quad core Intel Core i5-4440 (-MCP-) cache: 6144 KB clock speeds: max: 3300 MHz 1: 2711 MHz 2: 2599 MHz 3: 2692 MHz 4: 2573 MHz Graphics: Card: Advanced Micro Devices [AMD/ATI] Juniper XT [Radeon HD 5770] Display Server: X.Org 1.18.4 drivers: ati,radeon (unloaded: fbdev,vesa) Resolution: 1920x1080@60.00hz GLX Renderer: Gallium 0.4 on AMD JUNIPER (DRM 2.49.0 / 4.10.0-32-generic, LLVM 4.0.0) GLX Version: 3.0 Mesa 17.0.7 Audio: Card-1 Intel 8 Series/C220 Series High Definition Audio Controller driver: snd_hda_intel Card-2 Advanced Micro Devices [AMD/ATI] Juniper HDMI Audio [Radeon HD 5700 Series] driver: snd_hda_intel Sound: Advanced Linux Sound Architecture v: k4.10.0-32-generic Network: Card: Intel Ethernet Connection I217-V driver: e1000e IF: enp0s25 state: up speed: 1000 Mbps duplex: full mac: bc:5f:f4:ab:e1:39 Drives: HDD Total Size: 1901.6GB (1.6% used) ID-1: /dev/sda model: Samsung_SSD_840 size: 120.0GB ID-2: /dev/sdb model: WDC_WD10EZEX size: 1000.2GB ID-3: /dev/sdc model: SAMSUNG_HD753LJ size: 750.2GB ID-4: USB /dev/sdd model: Storage_Device size: 31.2GB Partition: ID-1: / size: 20G used: 9.5G (52%) fs: ext4 dev: /dev/sda3 ID-2: /home size: 46G used: 6.4G (15%) fs: ext4 dev: /dev/sdb3 ID-3: swap-1 size: 4.09GB used: 0.19GB (5%) fs: swap dev: /dev/sdb5 RAID: No RAID devices: /proc/mdstat, md_mod kernel module present Sensors: System Temperatures: cpu: 38.0C mobo: N/A gpu: 37.0 Fan Speeds (in rpm): cpu: N/A Info: Processes: 226 Uptime: 15:19 Memory: 2554.5/3866.3MB Client: Shell (bash) inxi: 2.2.35 Apparently, it's Cinnamon itself. It's a bit hard to capture the spike while also causing it, but Cinnamon's CPU usage increases to 40-60% during them, while no other process changes. PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 1719 ezio 20 0 2587952 600112 50384 S 16,3 15,2 137:58.43 cinnamon 983 root 20 0 283508 7944 5652 S 1,7 0,2 18:45.15 polkitd 19103 ezio 20 0 3388232 787320 148876 S 1,7 19,9 16:42.69 Web Content 1259 root 20 0 477696 128816 95528 S 1,0 3,3 9:09.57 Xorg 798 message+ 20 0 44196 4416 3128 S 0,7 0,1 7:41.66 dbus-daemon 840 root 20 0 450548 11984 10408 S 0,7 0,3 8:10.89 NetworkManager 25137 ezio 20 0 499564 40600 24392 S 0,7 1,0 0:08.13 gnome-terminal- 19052 ezio 20 0 3090968 688212 189464 S 0,3 17,4 14:53.08 firefox What could be the solution? Edit: In my journalct -e output, three lines caught my unprofesional eye: Aug 30 19:17:01 Cantabury CRON: pam_unix(cron:session): session closed for user root Aug 30 19:20:37 Cantabury cinnamon-screensaver-pam-helper: pam_ecryptfs: seteuid error Aug 30 19:20:37 Cantabury cinnamon-screensaver-pam-helper: gkr-pam: the password for the login keyring was invalid. Now that I see this, I recall gettingt a prompt several times complaining about the login keyring, asking for a password. I didn't know that password (it wasn't my user pw == the root pw), so just minimized/closed it.