linux-kernel - Re: Unified tracing buffer

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Message-ID: <33307c790809231238m1e80fef4rce8a80722ff245f1@mail.gmail.com>
Date:	Tue, 23 Sep 2008 12:38:36 -0700
From:	"Martin Bligh" <mbligh@...gle.com>
To:	"Thomas Gleixner" <tglx@...utronix.de>
Cc:	"Masami Hiramatsu" <mhiramat@...hat.com>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Mathieu Desnoyers" <compudj@...stal.dyndns.org>,
	"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, Sep 23, 2008 at 12:36 PM, Thomas Gleixner <tglx@...utronix.de> 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 !

We have linux patches that sync the TSC on exit_idle. I'll see if I can get
Michael to send them out.

M.
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