powernow regression in 8-STABLE

Jeremy Chadwick freebsd at jdc.parodius.com
Sat Jul 23 08:47:45 UTC 2011

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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