Date: Sat, 21 Jun 2003 08:43:15 +0200 From: Bruno Van Den Bossche <bruno.van.den.bossche@pandora.be> To: rhett@alasir.com Cc: current@freebsd.org Subject: Re: SMP & CPU_SUSP_HLT Message-ID: <20030621084315.582e64b1.bruno.van.den.bossche@pandora.be> In-Reply-To: <20030621014742.13635.qmail@web21505.mail.yahoo.com> References: <20030621014742.13635.qmail@web21505.mail.yahoo.com>
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On Sat, 21 Jun 2003 02:47:42 +0100 (BST) RMH <rmhlldr@yahoo.co.uk> wrote: > Hello gentlemen, > > it seems CPU_SUSP_HLT does nothing for SMP kernels. > > i386/i386/machdep.c: > > #ifdef SMP > static int cpu_idle_hlt = 0; > #else > static int cpu_idle_hlt = 1; > #endif > > It's noted that when enabled it will result in about 4.2% > loss in performance while doing buildworld. I haven't > checked with that, but I tested single-threaded applications > to suffer for about 2%, what shouldn't be a big difference. > > Beyond power consumption, suspend on HLT may solve some > overheating issues common for multiprocessor systems. At > least, it does so in my case. > > I suggest to remove #ifdef SMP, and place a warning into > NOTES. Let people decide. People can decide :-) You can set 'machdep.cpu_idle_hlt: 1' with sysctl. This will enable the hlt's for you. On single cpu-systems this is set by default. On SMP-systems it isn't, because of the "loss" in performance you already mentioned. -- Bruno Weinberg's Principle: An expert is a person who avoids the small errors while sweeping on to the grand fallacy.
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