public inbox for linux-tegra@vger.kernel.org
 help / color / mirror / Atom feed
From: Marc Dietrich <marvin24-Mmb7MZpHnFY@public.gmane.org>
To: "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Cc: Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>,
	Olof Johansson <olof-nZhT3qVonbNeoWH0uzbU5w@public.gmane.org>,
	Colin Cross <ccross-z5hGa2qSFaRBDgjK7y7TUQ@public.gmane.org>,
	Allen Martin <amartin-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
Subject: cpu clock change latency
Date: Fri, 23 Sep 2011 16:39:32 +0200	[thread overview]
Message-ID: <201109231639.33651.marvin24@gmx.de> (raw)

Hi,

arch/arm/mach-tegra/cpu-tegra.c (as from nv-tegra.nvidia.com) contains a some 
strange comment:

 493         /* FIXME: what's the actual transition time? */
 494         policy->cpuinfo.transition_latency = 300 * 1000;

The trees on chromeos.org (both, kernel and kernel-next) have:

 392         /* cpu clock change latency: ~400us */
 393         policy->cpuinfo.transition_latency = 400;

because according to 

http://git.chromium.org/gitweb/?p=chromiumos/third_party/kernel.git;a=commitdiff;h=6a4debe346f5946f4fab14b413885896b7cde324

this improves latency of the GUI. Note that the comment said "us", while the cpu 
transition latency is measured in "ns", so 400 * 1000 would be right. 

So either the comment is wrong (should be 400ns) or the patch is wrong (which is 
unlikely, because it improved latency in the testcase).

Can someone comment on this?

Thanks

Marc

             reply	other threads:[~2011-09-23 14:39 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-09-23 14:39 Marc Dietrich [this message]
     [not found] ` <201109231639.33651.marvin24-Mmb7MZpHnFY@public.gmane.org>
2011-09-23 16:44   ` cpu clock change latency Allen Martin
2011-09-23 16:49   ` Colin Cross
     [not found]     ` <CAMbhsRTiqLZ2bSefh-DnmDY0RB4JGkSmumh8Tt_7217BsHsa7Q-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2011-09-27 15:30       ` Mark Brown
     [not found]         ` <20110927153021.GA16150-GFdadSzt00ze9xe1eoZjHA@public.gmane.org>
2011-09-27 19:31           ` Marc Dietrich

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=201109231639.33651.marvin24@gmx.de \
    --to=marvin24-mmb7mzphnfy@public.gmane.org \
    --cc=amartin-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org \
    --cc=ccross-z5hGa2qSFaRBDgjK7y7TUQ@public.gmane.org \
    --cc=linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
    --cc=olof-nZhT3qVonbNeoWH0uzbU5w@public.gmane.org \
    --cc=swarren-DDmLM1+adcrQT0dZR+AlfA@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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox