3 ms·

> (those familiar know the hash-rate fluctuates and slows down towards the end) Could someone explain this to me, why does it slow down towards the end?

alex_duf 7y ago
I'm curious too, could it be due to the way the search space is explored in parallel?
parsimo2010 7y ago
I don't know for sure, but these Radeon GPUs are power hungry and hot. It could be just that after multiple days the entire computer is heat soaked and goes through more thermal throttling than even the "steady state" GPU tests that most gamers do (a few hours). It might also be cruft building up over time with small memory leaks or imperfect memory management.
- nexuist 7y ago
  This is what I thought too, the heat simply becomes overwhelming and the unit has to underclock to prevent melting.
  - close04 7y ago
    I think the "towards the end" part is the misleading one. The software has no idea where the end is or it would just jump there. Since the run took 4 days slowing down due to throttling would happen pretty fast as the card reaches a thermal equilibrium. Certainly wouldn't take days to do it. It's more likely the explanation above of something (not heat) accumulating over time and slowing down the processing.
    - floatboth 7y ago
      Real explanation below >> https://news.ycombinator.com/item?id=21205272 https://news.ycombinator.com/item?id=21205272
deleted 7y ago
[deleted]
jodrellblank 7y ago
For some context of how hashcat works with GPUs: https://hashcat.net/wiki/doku.php?id=frequently_asked_questions#how_to_create_more_work_for_full_speed https://hashcat.net/wiki/doku.php?id=frequently_asked_questi... Then: https://hashcat.net/wiki/doku.php?id=frequently_asked_questions#why_does_hashcat_sometimes_get_very_slow_at_the_end_of_an_attack https://hashcat.net/wiki/doku.php?id=frequently_asked_questi... It isn’t running a single thread at 100% GPU use until the end, it has to partition up the search space and balance how it creates possible passwords on the CPU, on the GPU, and based on the kind of attack patterns you asked for - and when it’s getting to the end of the search space, some of the search space partitions are done and the remaining ones aren’t enough to load the GPU fully, so hash throughout drops.
qot 7y ago
I suspect it's because the farther down the rule list you go, the more complicated the rules get. Password cracking often uses rule lists to modify known passwords lists in some way (adding 123 to the end, for example). These get more complicated towards the end so they take more operations.

alex_duf 7y ago

I'm curious too, could it be due to the way the search space is explored in parallel?

parsimo2010 7y ago

I don't know for sure, but these Radeon GPUs are power hungry and hot. It could be just that after multiple days the entire computer is heat soaked and goes through more thermal throttling than even the "steady state" GPU tests that most gamers do (a few hours). It might also be cruft building up over time with small memory leaks or imperfect memory management.

nexuist 7y ago
This is what I thought too, the heat simply becomes overwhelming and the unit has to underclock to prevent melting.
- close04 7y ago
  I think the "towards the end" part is the misleading one. The software has no idea where the end is or it would just jump there. Since the run took 4 days slowing down due to throttling would happen pretty fast as the card reaches a thermal equilibrium. Certainly wouldn't take days to do it. It's more likely the explanation above of something (not heat) accumulating over time and slowing down the processing.
  - floatboth 7y ago
    Real explanation below >> https://news.ycombinator.com/item?id=21205272 https://news.ycombinator.com/item?id=21205272

deleted 7y ago

[deleted]

jodrellblank 7y ago

For some context of how hashcat works with GPUs: https://hashcat.net/wiki/doku.php?id=frequently_asked_questions#how_to_create_more_work_for_full_speed https://hashcat.net/wiki/doku.php?id=frequently_asked_questi... Then: https://hashcat.net/wiki/doku.php?id=frequently_asked_questions#why_does_hashcat_sometimes_get_very_slow_at_the_end_of_an_attack https://hashcat.net/wiki/doku.php?id=frequently_asked_questi... It isn’t running a single thread at 100% GPU use until the end, it has to partition up the search space and balance how it creates possible passwords on the CPU, on the GPU, and based on the kind of attack patterns you asked for - and when it’s getting to the end of the search space, some of the search space partitions are done and the remaining ones aren’t enough to load the GPU fully, so hash throughout drops.

qot 7y ago

I suspect it's because the farther down the rule list you go, the more complicated the rules get. Password cracking often uses rule lists to modify known passwords lists in some way (adding 123 to the end, for example). These get more complicated towards the end so they take more operations.