linux-kernel - Re: Unified tracing buffer

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Date:	Mon, 22 Sep 2008 16:45:24 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	prasad@...ux.vnet.ibm.com
Cc:	Martin Bligh <mbligh@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Steven Rostedt <rostedt@...dmis.org>, od@...ell.com,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>, hch@....de,
	David Wilder <dwilder@...ibm.com>, zanussi@...cast.net
Subject: Re: Unified tracing buffer

On Mon, 2008-09-22 at 19:37 +0530, K.Prasad wrote:

> > > INPUT_FUNCTIONS
> > > ---------------
> > > 
> > > allocate_buffer (name, size)
> > >         return buffer_handle
> > > 
> > > register_event (buffer_handle, event_id, print_function)
> > >         You can pass in a requested event_id from a fixed set, and
> > > will be given it, or an error
> > >         0 means allocate me one dynamically
> > >         returns event_id     (or -E_ERROR)
> > > 
> > > record_event (buffer_handle, event_id, length, *buf)
> > 
> > I'd hoped for an interface like:
> > 
> > struct ringbuffer *ringbuffer_alloc(const char *name, size_t size);
> > void ringbuffer_free(struct ringbuffer *buffer);
> > int ringbuffer_write(struct ringbuffer *buffer, const char *buf, size_t size);
> > int ringbuffer_read(struct ringbuffer *buffer, int cpu, char *buf, size_t size);
> > 
> > On top of which you'd do the event thing, the register event with a
> > callback idea makes sense, except I'd split the consumption into two:
> >  - one method to pull the binary event out, which knows how long it
> > ought to be etc..
> >  - one method to convert the binary event to ASCII
> >
> In conjunction with the previous email on this thread
> (http://lkml.org/lkml/2008/9/22/160), may I suggest
> the equivalent interfaces in -mm tree (2.6.27-rc5-mm1) to be:
> 
> relay_printk(<some struct with default filenames/pathnames>, <string>,
> ....) ;
> relay_dump(<some struct with default filenames/pathnames>, <binary
> data>);
> and
> relay_cleanup_all(<the struct name>); - Single interface that cleans up
> all files/directories/output data created under a logical entity.

Dude, relayfs is such a bad performing mess that extending it seems like
a bad idea. Better to write something new and delete everything relayfs
related.

Also, it seems prudent to separate the ring-buffer implementation from
the event encoding/decoding facilities.



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