I've been experiencing this also. I can't tell you how frustrating it's been dealing with Nvidia over the last few days. I had one agent initially say they were aware of issues with multiple GPU setups and subsequent agents basically
behaved as if this was the first they were hearing about it. I have an open case (Case# 180803-000777) with them re. the matter.
Their current 'workaround' is to downgrade the driver. That's it. I've spent two days going back and forth with them on this. The last tech I chatted with was an engineer and recommended downgrading to 391.01. I did that and
ran my system on full load for some time without issue (100% on both CPU / GPU x3). Then the DPC Watchdog Violation happened again. I've since downgraded further to 382.53 and will report back here with any issues.
Thanks to all here for posting. Makes a big difference knowing that others are pushing for fix on this also.
My system specs...
i7 5960x 4.2 Ghz
64 GB memory
Asus X99 E WS motherboard
EVGA GeForce GTX 1080 SC GAMING ACX 3.0 (x 3)
Windows 10 Pro 64bit (1709)
Nvidia driver (now using 382.53)