4 ms·

HandBrake found me a defective RAM module on my PC: it freezed in the middle of video conversion - every single time on exactly the same video position. After f

by pulse7 10y ago

HandBrake found me a defective RAM module on my PC: it freezed in the middle of video conversion - every single time on exactly the same video position. After further investigation I found the "bug" in my RAM...

dvdhnt 10y ago
That's actually super interesting! I honestly wish I knew more about RAM to understand how that one process exposed the bug. :(
- pulse7 10y ago
  MemTest86 showed me my RAM is defect at exactly 1 bit: whatever you wrote to this bit, you got 0 back. During video conversion HandBrake used this part of RAM and could not cope with false data read from RAM... and froze... Since I used this machine to backup my data on DVDs I got many errors in my data on backup. But since I had a copy of everything on another HDD I throw the DVDs away and backed up everything again (after replacing defective RAM module and reinstalling OS and SW on my machine).
  - j1vms 10y ago
    > HandBrake used this part of RAM and could not cope with false data read from RAM Which in itself alludes to the encoding stream itself (or one of the intermediate streams during the encoding process) having some form of strong channel coding - in error detection - either by design or not. Detect 1-bit error in a gig+ stream, perhaps without easily being able to locate it, beyond saying it's in such or such chunk (the current frame(s) being processed).
brownbat 10y ago
Amazing. These are like Bill Brasky stories or Schneier facts. If Handbrake fails, it's only because your hardware is broken.
- KevinEldon 10y ago
  It's funny you should say that because the one time Handbrake failed for me Bill Brasky showed me how to hand solder my CPU, and I'd be your aunt if it didn't fix Handbrake. Bill Brasky, RIP.
- deleted 10y ago
  [deleted]
chrisper 10y ago
How is that even possible with virtual memory and paging? Why would the same video data or whatever go to the same physical location every time?
- dahart 10y ago
  I can imagine bunches of possibilities. Paging can make things hard to predict, especially when multiple programs are allocating memory, but it doesn't make the system non-deterministic, nor does it make hitting the same physical address impossible. One possibility is that he didn't restart the program between retries, and the memory in question was already allocated. Another possibility is that he only ran handbrake and nothing else, and the OS was in more or less the same state both times. It could be that the problem was triggered by stack allocations rather than heap allocations and the video block in question caused a large-ish recursion that hit the problem, and would be likely to hit the problem no matter what was running since it's somewhat rare to have large stack allocations. Chances are it was actually none of those things, but they're real possibilities anyway.
  - sk5t 10y ago
    Presuming "frozen PC" means "unresponsive and must be forcibly rebooted, there would be no retrying with the program without restarting. What with Windows Update and the variety of other similar OS- and application-level auto-updaters, is getting the computer into a very similar state likely? I'm not sure but my gut says no. That said, at first I was imagining a desktop computer with 4 or 8 memory modules, but given a machine with just 2 modules, maybe it follows that one module usually gets filled with "core stuff" and the second, defective module somewhat infrequently sees "big user stuff" after the first module is filled, and I guess that isn't too much of a head-scratcher when it comes to identifying the source of the problem.
  - pulse7 10y ago
    Maybe my Handbrake installation was broken because of defective RAM - I don't know exactly... anyway: I found the problem was RAM and now it works...
77pt77 10y ago
Best way to find memory problems is intensive multi-threaded video transcoding and intensive compiling (say installing gentoo).
- tdkl 10y ago
  Or you know - running memtest86[1]. [1] http://www.memtest.org http://www.memtest.org
  - _joel 10y ago
    Indeed, I'm also a fan of http://www.advancedclustering.com/products/software/breakin/ http://www.advancedclustering.com/products/software/breakin/ - use it for soak testing systems before giving them real load
    - tdkl 10y ago
      Wow, this looks awesome, will definitely check it out, thanks.

by pulse7 10y ago

dvdhnt 10y ago

That's actually super interesting! I honestly wish I knew more about RAM to understand how that one process exposed the bug. :(

pulse7 10y ago
MemTest86 showed me my RAM is defect at exactly 1 bit: whatever you wrote to this bit, you got 0 back. During video conversion HandBrake used this part of RAM and could not cope with false data read from RAM... and froze... Since I used this machine to backup my data on DVDs I got many errors in my data on backup. But since I had a copy of everything on another HDD I throw the DVDs away and backed up everything again (after replacing defective RAM module and reinstalling OS and SW on my machine).
- j1vms 10y ago
  > HandBrake used this part of RAM and could not cope with false data read from RAM Which in itself alludes to the encoding stream itself (or one of the intermediate streams during the encoding process) having some form of strong channel coding - in error detection - either by design or not. Detect 1-bit error in a gig+ stream, perhaps without easily being able to locate it, beyond saying it's in such or such chunk (the current frame(s) being processed).

brownbat 10y ago

Amazing. These are like Bill Brasky stories or Schneier facts. If Handbrake fails, it's only because your hardware is broken.

KevinEldon 10y ago
It's funny you should say that because the one time Handbrake failed for me Bill Brasky showed me how to hand solder my CPU, and I'd be your aunt if it didn't fix Handbrake. Bill Brasky, RIP.
deleted 10y ago
[deleted]

chrisper 10y ago

How is that even possible with virtual memory and paging? Why would the same video data or whatever go to the same physical location every time?

dahart 10y ago
I can imagine bunches of possibilities. Paging can make things hard to predict, especially when multiple programs are allocating memory, but it doesn't make the system non-deterministic, nor does it make hitting the same physical address impossible. One possibility is that he didn't restart the program between retries, and the memory in question was already allocated. Another possibility is that he only ran handbrake and nothing else, and the OS was in more or less the same state both times. It could be that the problem was triggered by stack allocations rather than heap allocations and the video block in question caused a large-ish recursion that hit the problem, and would be likely to hit the problem no matter what was running since it's somewhat rare to have large stack allocations. Chances are it was actually none of those things, but they're real possibilities anyway.
- sk5t 10y ago
  Presuming "frozen PC" means "unresponsive and must be forcibly rebooted, there would be no retrying with the program without restarting. What with Windows Update and the variety of other similar OS- and application-level auto-updaters, is getting the computer into a very similar state likely? I'm not sure but my gut says no. That said, at first I was imagining a desktop computer with 4 or 8 memory modules, but given a machine with just 2 modules, maybe it follows that one module usually gets filled with "core stuff" and the second, defective module somewhat infrequently sees "big user stuff" after the first module is filled, and I guess that isn't too much of a head-scratcher when it comes to identifying the source of the problem.
- pulse7 10y ago
  Maybe my Handbrake installation was broken because of defective RAM - I don't know exactly... anyway: I found the problem was RAM and now it works...

77pt77 10y ago

Best way to find memory problems is intensive multi-threaded video transcoding and intensive compiling (say installing gentoo).

tdkl 10y ago
Or you know - running memtest86[1]. [1] http://www.memtest.org http://www.memtest.org
- _joel 10y ago
  Indeed, I'm also a fan of http://www.advancedclustering.com/products/software/breakin/ http://www.advancedclustering.com/products/software/breakin/ - use it for soak testing systems before giving them real load
  - tdkl 10y ago
    Wow, this looks awesome, will definitely check it out, thanks.