linux-kernel - Re: debugctl msr

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Date:	Sat, 22 Nov 2008 10:51:31 +0100
From:	Markus Metzger <markus.t.metzger@...glemail.com>
To:	eranian@...il.com
Cc:	"Metzger, Markus T" <markus.t.metzger@...el.com>,
	Markus Metzger <markus.t.metzger@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: debugctl msr

On Fri, 2008-11-21 at 23:47 +0100, stephane eranian wrote:


> With the current code base, ds.c can accept a pre-allocated buffer.
> However, it does
> some adjustments for alignment and size (multiple of PEBS record
> size). That means
> that the start and end of the buffer could be different from the area
> passed to ds_request_pebs().
> 
> To parse the buffer, a monitoring tools needs a start position and the
> number of samples. The start
> position can be expressed as an offset from the beginning of the
> perfmon buffer.  The ds.c interface
> currently only returns indexes for current position, threshold, and
> end. Those indexes are good enough
> to derived the number of samples. But I would need one call to return
> the byte offset from the original
> buffer, or the actual address (which perfmon could then convert back
> to an offset from its buffer).

ds_access() returns the pointer into the raw buffer at a given index.
For index 0, this is the beginning of the buffer.


I plan to replace the various access functions with a single one that
returns a const pointer to the configuration.

Something like:

struct ds_config {
  size_t number_of_records;
  size_t size_of_a_single_record;
  void *base;
  void *max;
  void *index;
  void *threshold;
};

const struct ds_config *ds_config_pebs(struct pebs_tracer *tracer);

For BTS, I would add functions to work on this struct and translate raw
entries into an architecture-independent format.
I'm not sure whether this would make sense for PEBS, as well.

Would you be OK with such a change?


thanks and regards,
markus.


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