Date: Sun, 09 Feb 2003 16:21:10 +0100 From: Marcin Dalecki <mdcki@gmx.net> To: David Schultz <dschultz@uclink.berkeley.edu> Cc: Adrian Chadd <adrian@freebsd.org>, Terry Lambert <tlambert2@mindspring.com>, Ray Kohler <ataraxia@cox.net>, freebsd-current@freebsd.org Subject: Re: Compiling with high optimization? Message-ID: <3E4671E6.8090000@gmx.net> In-Reply-To: <20030209150120.GA2263@HAL9000.homeunix.com> References: <20030208173756.GA56030@arkadia.nv.cox.net> <20030208232724.GA20435@HAL9000.homeunix.com> <3E459BF3.BB3FC381@mindspring.com> <20030209002542.GA20812@HAL9000.homeunix.com> <20030209141006.GB33928@skywalker.creative.net.au> <20030209150120.GA2263@HAL9000.homeunix.com>
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David Schultz wrote: > Strangely, gcc in FreeBSD 5.0 actually generates *slower* code > when compiling for more recent architectures than when compiling > for a 386. I don't know whether that is a bug in gcc or whether > gcc is using some fancy feature like SSE that the kernel handles > poorly on context switches. I think there was some discussion on > the lists about it earlier. The reason is that the optimization done by GCC are ill balanced. All the scheduling of instractions and what a not - which would be fine on a micro scope level is causing so much higher pressure on the CPUs caches that the code is actually loosing. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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