Re: [PATCH] ftrace: add an fsync tracer

[Arjan van de Ven <arjan@infradead.org>]

On Thu, 06 Nov 2008 13:55:38 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> On Wed, 2008-11-05 at 09:49 -0800, Arjan van de Ven wrote:
> > From 63c1b869d94eb31a98015af09fb24e22151f2f00 Mon Sep 17 00:00:00
> > 2001 From: Arjan van de Ven <arjan@linux.intel.com>
> > Date: Tue, 4 Nov 2008 21:08:11 -0800
> > Subject: [PATCH] ftrace: add an fsync tracer
> > 
> > fsync() (and its cousin, fdatasync()) are important chokepoints in
> > the kernel as they imply very expensive operations, both in terms
> > of filesystem operations (ext3 writes back its entire journal) as
> > well as the block layer (fsync() implies sending a cache flushing
> > barrier to the SATA/SCSI disk).
> > 
> > This tracer makes a log of which application calls fsync() on which
> > file, so that developers and others interested in finding these
> > choke points can locate them and fix them in the apps that call
> > this function.
> 
> Sorry, but I have to object to such single purpose tracers..
> 
> If we go this way we'll end up with a gazillion little tracers, non of
> which are really useful.
> 
> Please work on getting something like a syscall tracer, or lttng like
> event tracer.
> 

btw a syscall tracer is not long term right, just like system call
level auditing was the wrong thing: you don't have the real information
of what's being worked on. having the trace points on the do_FOO()
level is the right thing, and that's exactly what my patch does.