linux-kernel - Hyperthreading on Core i7s: To use or not to use?

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Message-ID: <alpine.DEB.2.00.1001260456210.14707@p34.internal.lan>
Date:	Tue, 26 Jan 2010 05:02:08 -0500 (EST)
From:	Justin Piszcz <jpiszcz@...idpixels.com>
To:	linux-kernel@...r.kernel.org
Subject: Hyperthreading on Core i7s: To use or not to use?

Hello,

Should the 'correct' kernel [CPU] configuration for a core i7 860/870..?

- Multi-core support
- Cores: 8
- SMT: Enabled/ON

>From CONFIG_SCHED_SMT:

   . SMT scheduler support improves the CPU scheduler's decision making      .
   . when dealing with Intel Pentium 4 chips with HyperThreading at a        .
   . cost of slightly increased overhead in some places. If unsure say       .
   . N here.                                                                 .

Does this also 'help' and/or 'apply' as much when dealing with Core i7s?

--

Quick little benchmark (pbzip2 -9 linux kernel source), the benchmark is 
really within the noise (8 on/off)
- Multicore(8)/HT(Off) = 73.72user 0.33system 0:09.50elapsed 779%CPU (0avgtext+0avgdata 458528maxresident
- Multicore(8)/HT(On) = 74.28user 0.40system 0:09.67elapsed 772%CPU (0avgtext+0avgdata 428304maxresident
- Multicore(4)/HT(On) = 68.76user 0.30system 0:17.44elapsed 396%CPU (0avgtext+0avgdata 213616maxresident)k

--

Has anyone done any in-depth benchmarking for the core i7s that have multiple
cores and HT disabled/enabled?

Justin.
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