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Date: Mon, 23 May 2005 07:08:55 -0500 (CDT)
From: Sergey Babkin <babkin@verizon.net>
To: Stephan Uphoff <ups@tree.com>, Colin Percival <cperciva@freebsd.org>
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Cc: "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org>
Subject: Re: Re: Scheduler fixes for hyperthreading
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>> > Beside benchmarking - is there any other real use for RDTSC ?
>> 
>> Some (broken) software uses the TSC in combination with external events in
>> order to obtain entropy for cryptographic key generation.  As a result,
>> disabling RDTSC could lead to non-obvious but very problematic breakage.
>
>Both bde and phk seem to agree with you that just disabling RDTSC is not
>an option :-(

RDTSC is very useful for profiling. So given a choice
for disabling RDTSC or disabling hyperthreading
personally I'd have no doubts that disabling
hyperthreading wins.

So far I've seen no use for hyperthreading whatsoever.
If anything, it seems to make the machine slower
due to I think extra contention for memory/cache, and
probably due to the extra scheduling overhead.
So I just get it disabled in the BIOS.
Maybe I've just haven't seen the "right" kind of
applications.

-SB