LKML Archive on
help / color / mirror / Atom feed
From: Ingo Molnar <>
To: Karsten Wiese <>
Subject: Re: [PATCH -rt 2/3] Make trace_freerunning work
Date: Tue, 5 Dec 2006 23:10:46 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

* Karsten Wiese <> wrote:

> Only reorder trace entries once if trace_freerunning is 1. Modify 
> user_trace_stop() not to check report_latency(delta) then. Note that 
> at least MAX_TRACE entries must have been generated between 
> user_trace_start() and user_trace_stop() for a freerunning trace to be 
> reliable.

my thinking behind the freerunning feature is this:

freerunning should behave the same way with regard to latency 
measurement. I.e. report_latency() is still needed, and the kernel will 
thus do a maximum search over all traces triggered via start/stop.

the difference is in the recording of the last-largest-latency:

- with !freerunning, the tracer stops recording after MAX_TRACE entries, 
  i.e. the "head" of the trace is preserved in the trace buffer.

- with freerunning, the tracer never stops, it 'wraps around' after 
  MAX_TRACE entries and starts overwriting the oldest entries. I.e. the  
  "tail" of the trace is preserved in the trace buffer.

depending on the situation, freerunning or !freerunning might be the 
more useful mode.

but there should be no difference in measurement.

could you try to rework this patch with the above functionality in mind? 
(or if you'd like to see new functionality, what would that be - and we 
could/should implement that separately from the existing semantics of 
freerunning and !freerunning)


       reply	other threads:[~2006-12-05 22:11 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
2006-12-05 22:10 ` Ingo Molnar [this message]
2006-12-06 15:08   ` [PATCH -rt 0/3] Make trace_freerunning work; Take 2 Karsten Wiese
2006-12-06 15:12     ` [PATCH -rt 1/3] Make trace_freerunning work; Take 2: Off by 1 tweaks Karsten Wiese
2006-12-06 15:18       ` [PATCH -rt 2/3] Make trace_freerunning work; Take 2: Add atomic_t underrun Karsten Wiese
2006-12-06 15:26         ` [PATCH -rt 3/3] Make trace_freerunning work; Take 2: change reset_trace_idx() Karsten Wiese
2006-12-06 15:54     ` [PATCH -rt 0/3] Make trace_freerunning work; Take 2 Ingo Molnar

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:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \
    --subject='Re: [PATCH -rt 2/3] Make trace_freerunning work' \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).