Date: Sat, 23 Jul 2011 01:47:21 -0700 From: Jeremy Chadwick <freebsd@jdc.parodius.com> To: Callum Gibson <callumgibson@optusnet.com.au> Cc: Attilio Rao <attilio@freebsd.org>, freebsd-amd64@freebsd.org, freebsd-stable@freebsd.org, Jung-uk Kim <jkim@freebsd.org>, John Baldwin <jhb@freebsd.org> Subject: Re: powernow regression in 8-STABLE Message-ID: <20110723084721.GA7931@icarus.home.lan> In-Reply-To: <20110723081304.GA14172@omma.gibson.athome> References: <20110719112033.GA51765@omma.gibson.athome> <20110721205600.GA52261@omma.gibson.athome> <20110721214310.GA74656@icarus.home.lan> <201107220816.52901.jhb@freebsd.org> <20110723081304.GA14172@omma.gibson.athome>
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On Sat, Jul 23, 2011 at 06:13:04PM +1000, Callum Gibson wrote:
> On 22Jul11 08:16, John Baldwin wrote:
> }The problem is that we calibrate the TSC using this algorithm:
> }
> } - grab the TSC
> } - spin on the ISA timer waiting for it to run for a second
> } - grab the TSC
> }
> }The issue is that the SMI# fires at the same time we want to be execuiting
> }step 3, and step 3 is deferred while the SMI# handler runs. As a result, the
> }TSC delta ends up being "1 second + time of an SMI# to poll USB". We have a
> }hack fix for this at work that originally came from Attilio Rao. This is a
> }patch for it relative to 8. It disables interrupt generation for the ISA
> }timer while we calibrate the TSC (which disables the SMI# temporarily):
>
> Thanks, John. The hack works as intended, but I guess it's not a "real"
> solution which is why you haven't committed it?
This sort of thing is going to have to get dealt with officially sooner
or later, hack-fix or elegant solution either way[1].
More and more systems are using native USB keyboards, and most system
BIOSes I've seen (from multiple vendors, specifically Supermicro,
Lenovo, Asus, Dell, HP, and Gigabyte[2]) are defaulting to having these
options enabled (and rightfully so).
If the hack-fix has repercussions, it would be helpful to know what
those are or how those might manifest themselves. Otherwise, has anyone
taken a look at how Linux addresses this problem? To my knowledge GRUB
and similar bootstraps do not have a native USB stack, so I'm left
wondering how they deal with this.
[1]: I'm in no way saying "Hey! Fix this! {contributes nothing}", I'm
simply pointing out that we're at a point where we really don't have
much of a choice. The more I read technical explanations from John the
more hate x86 architecture. ;-)
[2]: On a couple Gigabyte boards I have the default values for said
option is enabled (for both keyboard and mouse).
--
| Jeremy Chadwick jdc at parodius.com |
| Parodius Networking http://www.parodius.com/ |
| UNIX Systems Administrator Mountain View, CA, US |
| Making life hard for others since 1977. PGP 4BD6C0CB |
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