linux-kernel - Re: Unified tracing buffer

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Date:	Tue, 23 Sep 2008 22:08:25 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Masami Hiramatsu <mhiramat@...hat.com>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Martin Bligh <mbligh@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>, darren@...art.com,
	"Frank Ch. Eigler" <fche@...hat.com>,
	systemtap-ml <systemtap@...rces.redhat.com>
Subject: Re: Unified tracing buffer

On Tue, 23 Sep 2008, Masami Hiramatsu wrote:

> Thomas Gleixner wrote:
> > On Tue, 23 Sep 2008, Masami Hiramatsu wrote:
> >> # cat /sys/devices/system/cpu/cpu0/cpuidle/state3/usage
> >> 171210
> > 
> > C3 stops the TSC. So depending on how many C3 entries you have on the
> > different cores, your TSCs will drift apart. Some BIOSes do even a
> > lousy job trying to fixup the TSCs on exit from C3, which makes things
> > even worse.
> > 
> >>     C1:                  type[C1] promotion[--] demotion[--] latency[001] usage[00000016] duration[00000000000000000000]
> >>     C2:                  type[C2] promotion[--] demotion[--] latency[001] usage[00037969] duration[00000000000024288003]
> >>     C3:                  type[C3] promotion[--] demotion[--] latency[057] usage[00171818] duration[00000000001881257636]
> >>
> >> Could these help you?
> > 
> > Yup, explains your TSC observation. Nothing we can do about. Broken by
> > system design :( Welcome in the wonderful world of Inhell/BIOS/ACPI !
> 
> Thank you for analyzing! :-)
> Hmm, then could I fix that by fixing my dsdt...?

You can limit c-states so you dont do down to the C3 state, but there
is a trade off vs. power saving.

Lets wait for Martins magic TSC patches first :)

     tglx
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