Date: Sun, 30 Oct 2005 23:58:43 -0800 From: "David O'Brien" <obrien@freebsd.org> To: Scott Long <scottl@samsco.org> Cc: Alexander Leidinger <Alexander@Leidinger.net>, freebsd-current@freebsd.org, David Xu <davidxu@freebsd.org> Subject: Re: TSC instead of ACPI: powerd doesn't work anymore (to be expected?) Message-ID: <20051031075843.GF39253@dragon.NUXI.org> In-Reply-To: <4364D90F.3090205@samsco.org> References: <30595.1130493297@critter.freebsd.dk> <20051028153457.d0wqgn2ask4sgw4k@netchild.homeip.net> <20051029195703.GB39253@dragon.NUXI.org> <43646AAC.2080107@freebsd.org> <20051030093718.GE39253@dragon.NUXI.org> <4364D90F.3090205@samsco.org>
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On Sun, Oct 30, 2005 at 07:30:39AM -0700, Scott Long wrote: > David O'Brien wrote: > >On Sun, Oct 30, 2005 at 02:39:40PM +0800, 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, > > > >Correct, but why is it felt the latency of the ACPI timer is an issue? > >Of course we all want things to as fast as possible, but is that just an > >abstract desire, or a real issue was run into? > > ACPI-fast requires an ioport read which takes about 1us (according to > Google). Do that 1000 times a second and you have each CPU spending > 1% of its time doing nothing but reading the clock. Yikes. But we've lived with using the ACPI timercounter (vs. TSC) for quite a while now. Why all of a sudden are the authors of this thread having an issue with it now. I know about the recent MySQL thread - but with the TSC being untrustable on MP and power managed systems, why is there such a desire to use the TSC? -- -- David (obrien@FreeBSD.org)
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