Re: [PATCH 00/14] xfs: Remove unused trace events

[Steven Rostedt]

On Mon, 16 Jun 2025 07:31:19 +0200
Christoph Hellwig <hch@xxxxxx> wrote:

> > I just did an analysis of this:
> > 
> >   https://lore.kernel.org/lkml/20250613104240.509ff13c@xxxxxxxxxxxxxxxxx/T/#md81abade0df19ba9062fd51ced4458161f885ac3
> > 
> > A TRACE_EVENT() is about 5K, and each DEFINE_EVENT() is about 1K.  
> 
> That's really quite expensive.  And you only measured the tezt/data/bss

Yes. This is something I've spent a bit of time over the years trying
to address. With moving a bunch of code into trace_event.c with the
added expense that trace events do function calls.

It looks like it's still growing as the last time I checked it was just
under 5K (something around 4800 bytes) and now it's over 5K, and the
tracepoint code grew 4x. I'll start looking into "why" later when I
have more time to deal with this. My time budget for removing unused
events has pretty much dried up.

> overhead and not even the dynamic memory overhead, which is probably
> a lot more.

Yes, and this is another area I look to make better. It was the
motivation for eventfs which saved over 20 megs of memory by having
trace event files dynamically created instead of being permanent.

-- Steve