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List:       fedora-devel-list
Subject:    Re: btrfs hash algorithm (should xxhash be the default?)
From:       drago01 <drago01 () gmail ! com>
Date:       2021-02-01 14:16:32
Message-ID: CAMqY-FeEvsJmZjW2g79ai0STAHxDE_K3ZYgyatVVnp56YQmVkg () mail ! gmail ! com
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On Sunday, January 31, 2021, Matthew Miller <mattdm@fedoraproject.org>
wrote:

> On my Intel i7 laptop, xxhash is a small but clear performance win over
> crc32c:
>
>     $ ./hash-speedtest  10000000
>     Block size:     4096
>     Iterations:     10000000
>     Implementation: builtin
>
>         NULL-NOP: cycles:   1372543560, c/i      137
>      NULL-MEMCPY: cycles:   2844174884, c/i      284
>           CRC32C: cycles:   9673117404, c/i      967
>           XXHASH: cycles:   7129819594, c/i      712
>           SHA256: cycles: 649914613520, c/i    64991
>          BLAKE2b: cycles: 153513008046, c/i    15351
>
>
> And I'm given to understand that this is even more the case on newer CPUs.
>
> Plus, it's 64 bit instead of 32 bit. The 256-bit algorithms are obviously
> much, much slower and probably not right for a default, but should we
> consider making xxhash the default for Fedora Linux systems with btrfs?
>
>
Comparing the hash algorithms in isolation doesn't mean much - does it make
a difference if you try various file system workloads with the different
algorithms?



> --
> Matthew Miller
> <mattdm@fedoraproject.org>
> Fedora Project Leader
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>

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<br><br>On Sunday, January 31, 2021, Matthew Miller &lt;<a \
href="mailto:mattdm@fedoraproject.org">mattdm@fedoraproject.org</a>&gt; \
wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px \
#ccc solid;padding-left:1ex">On my Intel i7 laptop, xxhash is a small but clear \
performance win over<br> crc32c:<br>
<br>
      $ ./hash-speedtest   10000000<br>
      Block size:        4096<br>
      Iterations:        10000000<br>
      Implementation: builtin<br>
<br>
            NULL-NOP: cycles:     1372543560, c/i         137<br>
        NULL-MEMCPY: cycles:     2844174884, c/i         284<br>
               CRC32C: cycles:     9673117404, c/i         967<br>
               XXHASH: cycles:     7129819594, c/i         712<br>
               SHA256: cycles: 649914613520, c/i      64991<br>
              BLAKE2b: cycles: 153513008046, c/i      15351<br>
<br>
<br>
And I&#39;m given to understand that this is even more the case on newer CPUs.<br>
<br>
Plus, it&#39;s 64 bit instead of 32 bit. The 256-bit algorithms are obviously<br>
much, much slower and probably not right for a default, but should we<br>
consider making xxhash the default for Fedora Linux systems with btrfs?<br>
<br></blockquote><div><br></div><div>Comparing the hash algorithms in isolation \
doesn&#39;t mean much - does it make a difference if you try various file system \
workloads with the different algorithms?</div><div><br></div><div>  </div><blockquote \
class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc \
                solid;padding-left:1ex">
-- <br>
Matthew Miller<br>
&lt;<a href="mailto:mattdm@fedoraproject.org">mattdm@fedoraproject.org</a>&gt;<br>
Fedora Project Leader<br>
______________________________<wbr>_________________<br>
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href="mailto:devel-leave@lists.fedoraproject.org">devel-leave@lists.<wbr>fedoraproject.org</a><br>
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 List Guidelines: <a href="https://fedoraproject.org/wiki/Mailing_list_guidelines" \
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 </blockquote>


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