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Message-ID: <20070407164915.GA4610@openwall.com>
Date: Sat, 7 Apr 2007 20:49:15 +0400
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: JTR use only 50% of my process on windows
On Wed, Apr 04, 2007 at 09:21:29AM -0500, RB wrote:
> Hyperthreading was a poor early answer by Intel to AMD's multi-core
> processors. It virtually 'splits' your processor in two, allowing two
> threads to think they're each consuming an entire processor, whereas
> in reality they're sharing the resources of one. IMHO, HT is
> worthless; I like to call it hardware-enforced preemption, as it makes
> everything slower to make stuff 'feel' more responsive. In your case,
> 50% utilization means that John is actually maxing out the processor.
Actually, Intel's Hyperthreading is not that bad. You've already
mentioned one of its advantages (over having a single-core CPU with no
HT or running a UP kernel) - better interactive response times. As it
relates to HT "making everything slower", this is only true for some
applications and some of their uses. In other cases, HT actually
improves performance. Speaking of John the Ripper, running two
instances of it on an HT-enabled P4 processor may result in an up to 30%
increase in c/s rate (for the two instances combined) at MD5-based
crypt(3) hashes. For other hash types, the increases are smaller. This
indicates that the code for MD5-based crypt(3) hashes that is currently
in John the Ripper is unoptimal for P4, though, and does not fully use
P4's execution units. Once this code is converted to use SSE2, the
advantage with HT should diminish.
--
Alexander Peslyak <solar at openwall.com>
GPG key ID: 5B341F15 fp: B3FB 63F4 D7A3 BCCC 6F6E FC55 A2FC 027C 5B34 1F15
http://www.openwall.com - bringing security into open computing environments
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