Date: Sun, 30 Oct 2005 07:03:57 -0700 From: Scott Long <scottl@samsco.org> To: David Xu <davidxu@freebsd.org> Cc: Alexander Leidinger <Alexander@Leidinger.net>, freebsd-current@freebsd.org Subject: Re: TSC instead of ACPI: powerd doesn't work anymore (to be expected?) Message-ID: <4364D2CD.6020406@samsco.org> In-Reply-To: <43646AAC.2080107@freebsd.org> References: <30595.1130493297@critter.freebsd.dk> <20051028153457.d0wqgn2ask4sgw4k@netchild.homeip.net> <20051029195703.GB39253@dragon.NUXI.org> <43646AAC.2080107@freebsd.org>
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David Xu wrote: > David O'Brien wrote: > >> On Fri, Oct 28, 2005 at 03:34:57PM +0200, Alexander Leidinger wrote: >> >> >>> I don't have the message at hand. I just had time to write the mail, >>> but I >>> don't have my laptop with me to reproduce the message. But it's easy to >>> reproduce, just take a PC which is able to make use of powerd and >>> switch to >>> using TSC as the timecounter. >>> >> >> >> What is the motivation to use the TSC as a timecounter? >> >> >> > TSC is faster than any others, on many systems, so-called ACPI-fast > timer is > really a slow chip, at least far slower than reading from RAM, > manufactories > just lie on this. > > Regards, > David Xu > Kind of. The TSC is internal to the CPU and can be read without any memory accesses or synchronization. The ACPI-faster counter needs to be read with an ioport instruction, which is exceedingly slow on modern hardware. ACPI-safe needs _three_ ioport reads. Scott
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