linux-kernel - Re: Perf can't deal with many tracepoints

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Date:	Thu, 28 Oct 2010 13:42:36 -0400
From:	fche@...hat.com (Frank Ch. Eigler)
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Perf can't deal with many tracepoints


"Theodore Ts'o" <tytso@....edu> writes:

> Perf will drop dead if it comes across tracepoints that have anything
> but primitive structure accessors in the TP_printk() section of the
> tracepoint definition.  For example, the ext4 and jbd2 tracepoints uses
> jbd2_dev_to_name() to translate a dev_t to a string.  

In the mean time, you may enjoy:

# stap -L 'kernel.trace("*")'
# stap -g -e '
%{
#include<linux/jbd2.h> 
%}
function jbd2name(dev) %{
   strlcpy(THIS->__retvalue, jbd2_dev_to_name(THIS->dev), MAXSTRINGLEN);
%}
probe kernel.trace("ext4_free_inode") {
   log(jbd2name($inode->i_sb->s_dev)) 
}'


> The block I/O tracepoints uses MAJOR() and MINOR() to translate a
> dev_t to a major/minor number pair.  [...]

(Similarly for this case.)


- FChE
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