Re: [patch 1/2] x86_64 page fault NMI-safe

From: Peter Zijlstra
Date: Wed Aug 04 2010 - 02:29:15 EST

On Tue, 2010-08-03 at 11:56 -0700, Linus Torvalds wrote:
> On Tue, Aug 3, 2010 at 10:18 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> > FWIW I really utterly detest the whole concept of sub-buffers.
> I'm not quite sure why. Is it something fundamental, or just an
> implementation issue?

The sub-buffer thing that both ftrace and lttng have is creating a large
buffer from a lot of small buffers, I simply don't see the point of
doing that. It adds complexity and limitations for very little gain.

Their benefit is known synchronization points into the stream, you can
parse each sub-buffer independently, but you can always break up a
continuous stream into smaller parts or use a transport that includes
index points or whatever.

Their down side is that you can never have individual events larger than
the sub-buffer, you need to be aware of the sub-buffer when reserving
space etc..

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