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Re: Unified tracing buffer

From: "Martin Bligh" <mbligh at google dot com>
To: "Thomas Gleixner" <tglx at linutronix dot de>
Cc: "Masami Hiramatsu" <mhiramat at redhat dot com>, "Linus Torvalds" <torvalds at linux-foundation dot org>, "Mathieu Desnoyers" <compudj at krystal dot dyndns dot org>, "Linux Kernel Mailing List" <linux-kernel at vger dot kernel dot org>, "Steven Rostedt" <rostedt at goodmis dot org>, darren at dvhart dot com, "Frank Ch. Eigler" <fche at redhat dot com>, systemtap-ml <systemtap at sources dot redhat dot com>
Date: Tue, 23 Sep 2008 12:50:40 -0700
Subject: Re: Unified tracing buffer
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References: <33307c790809191433w246c0283l55a57c196664ce77@mail.gmail.com> <20080923150410.GA28341@Krystal> <48D90B84.4030905@redhat.com> <alpine.LFD.1.10.0809230847360.3265@nehalem.linux-foundation.org> <48D921B3.2060809@redhat.com> <alpine.LFD.1.10.0809231927060.2038@apollo.tec.linutronix.de> <48D93CAF.8070000@redhat.com> <alpine.LFD.1.10.0809232129280.2038@apollo.tec.linutronix.de> <33307c790809231238m1e80fef4rce8a80722ff245f1@mail.gmail.com> <alpine.LFD.1.10.0809232140090.2038@apollo.tec.linutronix.de>

>> > 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.
>
> Are you sure that they sync it precicely enough that there is no user
> space observable way of time going backwards between cores ?

I think the tolerance is about 500 cycles. If that's not sufficient, I guess
we'll have to either live with some slight misordering (which people have
pointed out is kind of inevitable anyway) on these broken machines?
It was sufficient for what we were using it for, but maybe not for everyone.

Follow-Ups:
- Re: Unified tracing buffer
  - From: Thomas Gleixner

References:
- Re: Unified tracing buffer
  - From: Mathieu Desnoyers
- Re: Unified tracing buffer
  - From: Masami Hiramatsu
- Re: Unified tracing buffer
  - From: Linus Torvalds
- Re: Unified tracing buffer
  - From: Masami Hiramatsu
- Re: Unified tracing buffer
  - From: Thomas Gleixner
- Re: Unified tracing buffer
  - From: Masami Hiramatsu
- Re: Unified tracing buffer
  - From: Thomas Gleixner
- Re: Unified tracing buffer
  - From: Martin Bligh
- Re: Unified tracing buffer
  - From: Thomas Gleixner

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