Bug#679094: linux-image-3.4-trunk-amd64: 3.2, 3.3 and 3.4 debian kernels lack latencytop support

[Martin Steigerwald <ms@teamix.de>]

Am Mittwoch, 27. Juni 2012 schrieb Ben Hutchings:
> On Tue, 2012-06-26 at 12:46 +0200, Martin Steigerwald wrote:
> [...]
> 
> > The current Debian kernels all lack latencytop support:
> [...]
> 
> > Please consider activating this support again.
> 
> What do you mean, 'again'?

I thought this was once working out of the box, but maybe that was at a time 
where I compiled my own kernels and had it enabled.

> > Otherwise someone who wants to use latencytop needs to recompile the
> > kernel which greatly reduces the usefulness of the latencytop package.
> 
> This costs 1680 or 3360 bytes of non-paged memory for every thread in
> the system (depending on word size), even if the feature is never
> actually used.  On my laptop, for example, this would be about a
> megabyte.  I really don't think this is a good idea.

I found out that it will need the framepointer stuff which makes the kernel 
slightly larger and slower only after writing the bug report.

While I do not care that much about the megabyte given current memory sizes, I 
am concerned about the "slightly slower". And then its declared as kernel 
hacking feature in the configuration anyway. And for older / embedded machines 
1 MiB might be much.

So I can understand your reasoning. Feel free to close as won't fix or 
"dependent / waiting for upstream fix" if thats possible.

> It is probably possible to change the way the latency records are kept
> so that this memory is allocated only when needed, but I'm unlikely to
> find the time to do that.

Care to elaborate on that one a bit. I am willing to open a upstream bug 
report about that and include your idea and a reference to this debian bug 
report.

Thanks,
-- 
Martin Steigerwald - teamix GmbH - http://www.teamix.de
gpg: 19E3 8D42 896F D004 08AC A0CA 1E10 C593 0399 AE90