[ale] Using the VT capability of the CPU...

[Michael B. Trausch]

On Sat, 2007-04-28 at 18:19 -0400, Michael B. Trausch wrote:

> Also, there was a bit of a performance issue with the kernel losing
> interrupts, but I found a post somewhere on the 'net (don't have the
> bookmark handy, unfortunately) that said to enable RTC emulation in
> the kernel to fix it and gain a significant amount of performance.  I
> am about to try it to see if it works the way the site said it would,
> because I rebuilt the kernel and flipped that on.


Well.  I have mucked around with that and I am really impressed.  I
found the the post with the information I referenced earlier, so I there
it is so that y'all can see it.

This does seem to significantly improve the performance, along with some
of the other modifications that I made to the kernel.  Specifically, I
enabled the low latency functionality and increased the timer frequency
from 250Hz to 1000Hz.  The sound from the Windows XP guest is no longer
clipping, and everything but the video performance is absolutely
amazing.  Of course, that means that I get better-than-QEMU performance
now, and that's wonderful.  Now if only QEMU would create a second
thread on SMP systems... :-)

There are a few other modifications, and the total difference from the
stock Ubuntu kernel is only 18 lines.  Basically, I made the kernel
fullly preemptive, reduced the number of supported processors to two
(since that's all that I have; theoretically this should reduce the
kernel's memory footprint, but I don't even know where to begin looking
for that type of information anymore...), enabled that RTC thing, and
made the kernel specific for AMD64 systems as opposed to generic support
for both EM64T and AMD64.  All in all, the difference is extremely
noticeable.

In case anyone is interested, I am attaching a gzip'd unified diff of
the configuration differences.  Perhaps someone will benefit from them,
or be able to tweak them further for their own use.

    -- Mike

--
Michael B. Trausch
                    fd0man at gmail.com
Phone: (404) 592-5746
                          Jabber IM:
                    fd0man at gmail.com
              fd0man at livejournal.com
Demand Freedom!  Use open and free protocols, standards, and software!
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