Re: [RFC PATCH 1/3] Unified trace buffer

[Linus Torvalds <torvalds@linux-foundation.org>]

On Thu, 25 Sep 2008, Mathieu Desnoyers wrote:
> 
> We could use a page header instead to contain the "unused_size"
> information.

Absolutely. There's no one way to do this.

> I would prefer to put the extended timestamp within the event header
> instead of creating a separate entry for this for atomicity concerns
> (what happens if a long interrupt executes between the TSCExtend marker
> event and the event expecting to be written right next to it ?).

The log entries should be reserved with interrupts disabled anyway, and 
they are per-CPU, so there are no atomicity issues.

For NMI's, things get more exciting. I'd really prefer NMI's to go to a 
separate ring buffer entirely, because otherwise consistency gets really 
hard. Using lockless algorithms for a variable-sized pool of pages is a 
disaster waiting to happen.

I don't think we can currently necessarily reasonably trace NMI's, but 
it's something to keep in mind as required support eventually.

		Linus