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Date: Wed, 5 Sep 2012 07:33:20 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: memory usage (was: [john-users] JTR against 135 millions MD5 hashes)
On Tue, Sep 04, 2012 at 05:06:38AM -0400, jfoug@....net wrote:
> Do the builds drop to binary align=1 on intel boxes? We probably
> should, or at least allow a compile define to get this, in case it
> causes a slight runtime slowdown. Even for salts, I think we should
> drop to align=1 on systems allowing non-aligned access, and fix any
> formats which core due to actually having alignment issues (such as SIMD
> access). The requires aligned systems (like sparc) but even there, it
> might be better to have the default be 1, and fix any format with
> issues. Possibly it would be better with more than 1 default value.
Currently, mem_alloc_tiny() has:
#if ARCH_ALLOWS_UNALIGNED
if (mem_saving_level > 2)
align = MEM_ALIGN_NONE;
#endif
So alignments are only disabled at the heaviest memory saving level,
along with other performance-killing. Maybe we should adjust this -
what happens at what memory saving level - although it'd be good to do
some performance testing first.
I don't like the idea of disabling the alignments at compile time.
Alexander
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