lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Sat, 14 Jun 2014 23:19:13 -0400
From:	Theodore Ts'o <>
To:	Linux Kernel Developers List <>,
	George Spelvin <>
Subject: Re: Surprising 64-bit performance anomaly (was Re: [PATCH] random:
 use an improved fast_mix() function)

On Sat, Jun 14, 2014 at 11:04:41PM -0400, Theodore Ts'o wrote:
> Hi George,
> On top of the above patch, I applied the following to add 64-bit pool
> support.  I had to use a union to avoid type punning warnings.
> When building a 64-bit kernel and running under under KVM, I'm finding
> that the 64-bit mix function which you suggested is twice as slow.
> Using the (new) 32-bit function:
> 31821 23970
> 31629 24366
> 30856 24182
> Using the 64-bit mixing function:
> 60438 44369
> 60820 45402
> 58778 45419

I'm now getting a different set of timing numbers for the 64-bit
mixing function.  As before the first number is the weighted moving
average; the second is the deviation:

48035 34322
47452 34413
46974 34350

I'm not sure why I'm getting slightly better figures now, but it's
still worse than the 32-bit fast_mix3() algorithm.  Also, given the
additional complexity I'm not sure it's worth it to have a different
mixing algorithm for 64-bit platforms, unless it's significantly
better, and right now, I'm seeing numbers which are about 50% worse,
at least on my test platform.

	   	      	      	   	      - Ted
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

Powered by blists - more mailing lists