Intrepid vs. Jaunty kernels (monolithic vs. built-in)

[Scott James Remnant]

It's also worth comparing the Intrepid and Jaunty kernels in general.
This has some key figures because we're switching to more modules
built-in than before.

To try and split the difference, I built two "jaunty" kernels: 2.6.28-3
is from GIT just before the configs were changed; 2.6.28-4 is current
GIT HEAD.

This isn't 100% fair, since other changes have happened between the
kernels, but it's close as feel like getting ;)


Bear in mind that 2.6.28-4 also includes the change to reduce the legacy
pty count to zero, so that will affect various numbers.


Average processing times between kernel uevent and udev completion:

	2.6.27-9	2.6.28-3	2.6.28-4
MEAN	6.88s		7.81s		5.01s
MEDIAN	8.07s		8.87s		5.55s
MODE	8.13s		2.80s		5.28s
STDDEV	2.44s		2.67s		2.95s


Interesting that 2.6.28 seems to take rather longer, with a much reduced
mode (most common figure), and that 2.6.28-4 undoes that to make it
generally faster again.

Numbers are comparable to the legacy pty change, which isn't totally
surprising really - the behemoth of module pain (ALSA) is still a
module.


General instrumenting:

			2.6.27-9	2.6.28-3	change		2.6.28-4	change		total change
udev in initramfs:	 0.01s		 0.02s		+0.01s (200%)	 0.01s		-0.01s (50%)	 0     (100%)
udev in system:		 0.05s		 0.04s		-0.01s (80%)	 0.04s		 0     (100%)	-0.01s (80%)

trigger in initramfs:	 0.29s		 0.22s		-0.07s (75%)	 0.09s		-0.13s (40%)	-0.20s (31%)
trigger in system:	 0.60s		 0.24s		-0.36s (40%)	 0.16s		-0.08s (66%)	-0.44s (26%)

processing in initramfs: 2.58s		 3.82s		+1.24s (148%)	 2.25s		-1.57s (58%)	-0.33s (87%)
processing in system:	10.45s		11.86s		+1.41s (113%)	 9.37s		-2.49s (79%)	-1.08s (89%)

time in kernel:		 2.61s		 2.61s		 0     (100%)	 2.63s		+0.02s (100%)	+0.02s (100%)
time in initramfs:	 3.59s		 4.56s		+0.97s (127%)	 2.96s		-1.60s (64%)	-0.63s (82%)
(of which udev)		   71%		   83%				   76%
time booting system:	25.65s		26.45s		+0.80s (103%)	21.54s		-4.91s (81%)	-4.11s (83%)
(of which udev)		   40%		   44%				   43%

Again we see that 2.6.28 takes longer than 2.6.27, not just in the
system (which we could blame on readahead) but in initramfs as well.
More to do, maybe?

We then see that more things as built-ins certainly reduces lots of
overhead.  The udevadm settle in initramfs drops by a third of a second,
and the one in the main system by over a seccond.

In total, the system comes up almost five seconds quicker.

What's really interesting here is that the time in kernel doesn't seem
to change at all - even with the built-ins, the initramfs starts at
basically the same clock time.


Scott
-- 
Scott James Remnant
scott at canonical.com
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