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Re: [PATCH, RFC] xfs: event tracing support

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH, RFC] xfs: event tracing support
From: Felix Blyakher <felixb@xxxxxxx>
Date: Mon, 22 Jun 2009 16:37:12 -0500
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>, xfs@xxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx
In-reply-to: <20090622205904.GA1855@xxxxxxxxxxxxx>
References: <20090616214844.GA12310@xxxxxxxxxxxxx> <4E752C93-A674-4725-AF23-C227C0A1E659@xxxxxxx> <20090622205904.GA1855@xxxxxxxxxxxxx>

On Jun 22, 2009, at 3:59 PM, Christoph Hellwig wrote:

On Mon, Jun 22, 2009 at 01:01:35PM -0500, Felix Blyakher wrote:
To use it make sure CONFIG_EVENT_TRACING is enabled and then enable
xfs trace channels by:

 echo 1 > /sys/kernel/debug/tracing/events/xfs/enable

Does event tracing work on ia64 platform?
I spent some time on it over weekend, but was not able even
to force "CONFIG_EVENT_TRACING=y" setting in the .config.
Seems to build ok on x86_64, which does have CONFIG_TRACING
in defconfig, and allows to set CONFIG_EVENT_TRACING.

IA64 ftrace support was added earlier this year, but it seems it can't
be enabled anymore since the big config option reshuffle.  Now tracing
support requires the architecture to define the TRACE_IRQFLAGS_SUPPORT
and STACKTRACE_SUPPORT symbols, which seems to be missing on ia64.

That's what I found.
What would it take to add ftrace support on IA64?

If tracing is not available on all platforms, especially
on ia64, which is one of preferred platforms at SGI, we need
to preserve the original XFS tracing facilities. I know, it'll
be PIA to keep both tracing methods, but we can't drop
the working feature without good replacement.

It's not working at all in mainline and never had.  And for about
a year thaere hasn't been any tree around that actuall supports it..

True. But with simple patch (basically restoring xfsidbg.c) and
adding kdb support I was using xfs trace successfully. I know,
it doesn't help much if it's not in the mainline, but it's
real working code. Btw, that helped me recently identify the
deadlock in xfs_growfs (xfs qa test 104). I'll post those to
the xfs list or bugzilla shortly.

I hope tracing support for ia64 could be added, and this
issue won't be a showstopper.


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