Date: Sat, 04 Oct 2003 22:56:27 +0100 From: Ian Dowse <iedowse@maths.tcd.ie> To: Kris Kennaway <kris@obsecurity.org> Cc: freebsd-hackers@freebsd.org Subject: Re: Hyperthreading slowdown Message-ID: <200310042256.aa22200@salmon.maths.tcd.ie> In-Reply-To: Your message of "Sat, 04 Oct 2003 13:04:35 PDT." <20031004200435.GA60432@rot13.obsecurity.org>
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In message <20031004200435.GA60432@rot13.obsecurity.org>, Kris Kennaway writes: >Yes, that's because (as discussed in the archives) the kernel treats >it like an extra, completely decoupled physical CPU and schedules >processes on it without further consideration. This is presumably the >cause of the slowdown, because it's only efficient to use the virtual >CPU under certain workload patterns. HTT is not magic performance >beans. Try also setting the sysctl variable "machdep.cpu_idle_hlt" to 1, as it doesn't help to have the idle logical CPUs spinning. Ian
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