Re: architectures that prevent freezing
Re: architectures that prevent freezing
- Subject: Re: architectures that prevent freezing
- From: Wade Tregaskis <email@hidden>
- Date: Fri, 11 May 2012 14:49:29 -0700
>> While playing with GPU programming, I had a lot of such freeze, and they never locked the CPU. I was always able to connect to my machine though SSH.
Sometimes you can, sometimes you can't. It depends on exactly how things fail.
> So a regular user process can permanently lock up the display, requiring a reboot, just by executing some bad GPU code?! That’s kind of a bad privilege violation and could be considered a DoS exploit.
Yes, it is. A particularly serious one. It's been a pet peeve of mine for years that this is knowingly ignored by those who should know better.
Last I checked, there was a watchdog mechanism on the GPU that would fire after some time (7 seconds on nVidia GPUs). That signals the driver (on the CPU) that it's doing a watchdog reset. Unfortunately, the drivers don't really handle that. They could - and *should* - reinitialise and recover, but it's just not implemented (or at least wasn't, a year or two ago).
[[ There's probably also timeouts implemented in the driver and various other layers, though I don't know the details. ]]
If you've ever done any CUDA work you'll be all too familiar with this problem. Much of nVidia's own example code will trigger this failure mode, and most require a reboot to recover from.
In general GPUs are in a comparative stone-age when it comes to security and stability. They're getting better - retracing the steps of CPUs thirty years ago while thinking they're being very clever, in a cutely naive way - but it'll probably be many years before these problems are properly resolved.
AMD & Intel are significantly ahead of nVidia in this regard, I hear. But personally, after having every single nVidia-packing machine I've ever owned die (sometimes repeatedly) due to GPU-related hardware faults, I'd never buy an nVidia based machine to begin with. But I digress... back to trying to recover data from my 8800GS iMac... again...
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