From: Janosch Machowinski <scotch-cGBD8117FJM@public.gmane.org>
To: acpi-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
Subject: Re: Information regarding C3 cpu state and bus mastering activity
Date: Mon, 12 Dec 2005 13:51:58 +0100 [thread overview]
Message-ID: <439D726E.4020704@tzi.de> (raw)
In-Reply-To: <da5cd1900512120122y217541a2h-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
Marco Calviani wrote:
> Is this an hardware limitation or a software one?
> If i understood well this occur because the active bus polling that is
> required to maintain communication with usb devices deny the CPU from
> switching to C3, and even if there are no usb device connected but the
> modules are loaded the polling prevent the switch.
> Will it be possible to increase the polling time, so that maybe the
> CPU can enter that state?
>
Okay, I read through this stuff once again. I would say, that busmaster
activity is a direct write into memory. While the processor is in C3, it
can not keep it's cache in sync with the memory. So there are two
solutions to this problem for uniprocessor systems:
1. Either you flush the cache before entering C3. This takes a relative
long period of time (according to ACPI 3.0 spec) so it should not be the
prefered method.
2. Disable the busmaster. The kernel looks at the current busmaster
activity and then chooses if it wants to disable busmaster and enter C3.
After reading through the spec again, I would revoke my first comment
and say that with a bit of policytuning you could enter C3 even with a
USB mouse plugged in.
-------------------------------------------------------
This SF.net email is sponsored by: Splunk Inc. Do you grep through log files
for problems? Stop! Download the new AJAX search engine that makes
searching your log files as easy as surfing the web. DOWNLOAD SPLUNK!
http://ads.osdn.com/?ad_id=7637&alloc_id=16865&op=click
next prev parent reply other threads:[~2005-12-12 12:51 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-12-11 20:10 Information regarding C3 cpu state and bus mastering activity Marco Calviani
[not found] ` <da5cd1900512111210k626ff691x-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2005-12-12 0:33 ` Janosch Machowinski
[not found] ` <439CC549.5060500-cGBD8117FJM@public.gmane.org>
2005-12-12 3:42 ` Phillip Susi
[not found] ` <439CF197.3090902-3tLf1voIkJTQT0dZR+AlfA@public.gmane.org>
2005-12-12 12:47 ` Janosch Machowinski
[not found] ` <439D716B.3010705-cGBD8117FJM@public.gmane.org>
2005-12-12 16:08 ` Phillip Susi
2005-12-12 9:22 ` Marco Calviani
[not found] ` <da5cd1900512120122y217541a2h-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2005-12-12 12:51 ` Janosch Machowinski [this message]
[not found] ` <439D726E.4020704-cGBD8117FJM@public.gmane.org>
2005-12-12 16:02 ` Marco Calviani
2005-12-12 16:10 ` Marco Calviani
[not found] ` <da5cd1900512120810v75dd8721t-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2005-12-13 2:08 ` phutchis-CWA4WttNNZF54TAoqtyWWQ
[not found] ` <200512130208.jBD280VU003725-2ArO/UEyFsZWk0Htik3J/w@public.gmane.org>
2005-12-13 20:52 ` Marco Calviani
2005-12-13 14:06 ` Pavel Machek
[not found] ` <20051213140624.GA13694-I/5MKhXcvmPrBKCeMvbIDA@public.gmane.org>
2005-12-14 11:58 ` Erik Slagter
2005-12-14 21:29 ` Marco Calviani
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=439D726E.4020704@tzi.de \
--to=scotch-cgbd8117fjm@public.gmane.org \
--cc=acpi-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.