On Wed, Sep 30, 2020 at 10:30:57PM +0100, Laurence Tratt wrote: > For the past couple of weeks I've been encountering a weird problem on > -current amd64 -- my screen intermittently blanks for around 2-4 seconds > when running xorg. At first I thought this was a hardware problem (the > machine isn't a spring chicken), but then ffmpeg caught the blanking while > I was doing a screencast (i.e. the recording of the xorg part of things > goes entirely blank for a couple of seconds), so it seems to be a software > problem. > > Unfortunately I can't seem to find any obvious trigger. It seems to happen > more often when the machine is under heavy load, but sometimes it happens > under light load. Frankly, I don't have any real idea *what* could be > causing it, and I'm hoping that someone else might have seen this, and > perhaps have been equally baffled as to the cause!
I have now found a semi-reliable way of triggering this with the following ffmpeg command on a decent length video file: ffmpeg -i <video> -c:a flac out.flac The blanking effect is not consistent or continuous: sometimes the display will blank every few seconds, sometimes it might go 30 seconds without doing so. I'm running on a 4 core machine, and this task maxes out all 4 cores. Interestingly, however, other tasks which use all 4 cores do not cause the display blanking problem as often. I don't know what ffmpeg is doing differently, other than 'top' shows that it's often 'fsleep'ing (which may well be completely irrelevant to the problem I'm seeing). Laurie
