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jedisct1's profile
Frank
Frank
Frank
@jedisct1

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Frank

@jedisct1

France
Joined November 2008

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    1. Solar Designer‏ @solardiz 27 Jan 2018
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      @jedisct1 How much speedup did you get in recent libsodium due to MAP_POPULATE, presumably for Argon2 & scrypt when memory (de)allocation happens each time? I've just tried it for yescrypt on RHEL6 & 7, getting ~+3% on average (but more stable speeds), up to ~+10% for some sizes.

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    2. Frank‏ @jedisct1 27 Jan 2018
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      Replying to @solardiz

      ~5% with the default libsodium parameters on bare metal Arch/x86_64. Haven’t tried in a VM.

      1 reply 0 retweets 1 like
    3. Solar Designer‏ @solardiz 27 Jan 2018
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      Replying to @jedisct1

      Thanks. My tests were also on bare metal. Now I wish we had an equivalent flag for use along with shmget() IPC_CREAT, and ideally also a flag (or more?) to spread the allocation evenly across all NUMA nodes vs. keep it local to the current NUMA node (vs. indicate no preference?)

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    4. Solar Designer‏ @solardiz 6 Jun 2018
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      Replying to @solardiz @jedisct1

      Just found out that MAP_POPULATE results in a 7% regression for yescrypt at 2 MiB in multi-threaded benchmarks on RHEL6 when the memory allocation would be reused anyway - thus, where MAP_POPULATE was expected to neither help nor hurt. Now think how to skip it when it's unneeded.

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    5. Solar Designer‏ @solardiz 6 Jun 2018
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      Replying to @solardiz @jedisct1

      MAP_POPULATE appears to favor NUMA node 0 even for threads running on node 1. A benchmark limited to node 0 shows only a 2% regression (compared to no MAP_POPULATE), limited to node 1 shows 8%+ regression. Worse, intended use (allocations not reused) is hurt the most: 2x+. :-(

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    6. Solar Designer‏ @solardiz 6 Jun 2018
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      Replying to @solardiz @jedisct1

      None of this is seen from single-threaded benchmarks on idle machine. The adverse effects are progressively more noticeable with higher thread counts. Also, I don't recall seeing this on systems newer than RHEL/CentOS 6.x. Yet it's bad enough not to use MAP_POPULATE by default.

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    7. Solar Designer‏ @solardiz 6 Jun 2018
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      Replying to @solardiz @jedisct1

      The adverse effects vary greatly after making/freeing other large memory allocations. However, in all cases I tested today on this machine MAP_POPULATE either makes no difference (single-threaded) or hurts (multi-threaded). I am not able to get any speedup from it here anymore.

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    8. Solar Designer‏ @solardiz 7 Jun 2018
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      Replying to @solardiz @jedisct1

      Also got a 6% slowdown from MAP_POPULATE on RHEL7 (not 6) on a desktop machine (no NUMA) in multi-threaded KDF use case (1 GiB shared by 4 threads, memory (de)allocation inside the benchmark loop). With all of these results, I think I'll drop MAP_POPULATE from yescrypt releases.

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      Frank‏ @jedisct1 7 Jun 2018
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      Replying to @solardiz

      Fair enough. Thanks a lot for reporting this. I think I’m gonna keep it in sodium since it’s single threaded, but that’s definitely good to know.

      6:31 AM - 7 Jun 2018 from Paris
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        1. Solar Designer‏ @solardiz 7 Jun 2018
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          Replying to @jedisct1

          By multi-threaded, I mean not only use of multiple threads to derive one key, but also use of multiple threads or processes in the program to compute multiple single-threaded password hashes concurrently. Both are impacted, and surely the latter is relevant to sodium as well.

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