Date: Sun, 30 Oct 2005 07:30:39 -0700 From: Scott Long <scottl@samsco.org> To: freebsd-current@freebsd.org Cc: Alexander Leidinger <Alexander@Leidinger.net>, David Xu <davidxu@freebsd.org> Subject: Re: TSC instead of ACPI: powerd doesn't work anymore (to be expected?) Message-ID: <4364D90F.3090205@samsco.org> In-Reply-To: <20051030093718.GE39253@dragon.NUXI.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>
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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. Scott
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