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Re: Using debug and tracing features in 2.4.26

To: Steve Lord <lord@xxxxxxx>
Subject: Re: Using debug and tracing features in 2.4.26
From: Craig Tierney <ctierney@xxxxxxxx>
Date: Tue, 27 Apr 2004 14:18:26 -0600
Cc: linux-xfs@xxxxxxxxxxx
In-reply-to: <408EAC06.7010404@xxxxxxx>
References: <1083086648.2374.15.camel@xxxxxxxxxxxxxxxxxx> <408EAC06.7010404@xxxxxxx>
Sender: linux-xfs-bounce@xxxxxxxxxxx
On Tue, 2004-04-27 at 12:52, Steve Lord wrote:
> Craig Tierney wrote:
> > I have enabled debugging and tracing features in XFS
> > using the 2.4.26 kernel.  When I load the xfs module,
> > it reports that tracing and debugging are enabled.
> > 
> > (From dmesg)
> > SGI XFS with tracing, debug enabled
> > SGI XFS Quota Management subsystem
> > 
> > To enable tracing, the Configure.help file says to set
> > /proc/sys/vm/pagebuf/debug.  However, I could not find this
> > sysctl, or anything that was similar in the /proc/fs/xfs or
> > /proc/sys/fs/xfs directories.
> > 
> > How do I turn this on?
> > 
> > Also, with debugging enabled, do all debug messages go to the
> > kernel log?
> The tracing is to internal kernel buffers and is not much use
> unless you have a debugger capable of looking at them, which
> means kdb and the xfs support for kdb.
> Any reason for turning on debug? It adds thousands of checks to
> the code base, any one of them will oops if it triggers. Never
> run this way with data you care about.
> Steve

I am exporting my XFS filesystems over NFS.  Under load we are
seeing corruption on writes.  Corruption is in multiples of 4KB,
and are always paged aligned.  

I sent a post to the list last week:


Besides that post, it happens when kernel is booted as "nosmp,noapic",
and corruptions seems to happen more as the performance of the
server goes up.  I get more corruption for a given number of runs
on a Dual 2.6Ghz Xeon than on a Dual 933Mhz PIII.

I was able to generate corrupted output with debugging enabled, but
no oopses occurred.


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