[Buildroot] gunzip slows booting
msander at ripnet.com
Fri Jul 11 04:27:26 UTC 2008
I'm building a 2.6.25 kernel and initramfs for an atmel at91sam9260ek
using buildroot. I'm not sure if I'm experiencing a buildroot problem
per se, but hopefully someone here might have some insight.
With the default uImage (uses compressed zImage) and default compressed
initramfs I have a boot time from exiting u-boot to my user space
application running (started from iniittab) on the order of 3.0 sec.
If I generate the uImage from Image (uncompressed kernel image), my
boot time drops to approx 2.0 sec. As far as I can see, the only
difference is that gunzip() is not called for the uncompressed kernel.
It becomes a simple data copy. I don't have the image sizes at hand,
but gzip typically gives a 2:1 compression ratio.
Similarly, if I generate an uncompressed initramfs ( I simply removed
the gzip from gen_initramfs_list.sh) my boot time further drops to 1.2
sec. The filesystem is ~600k compressed and 1.3 MB uncompressed.
Again, the unzip is replaced by a data copy operation.
I guess the first question is whether there is a problem or not with
gzip appearing to be slow? I had expected the compressed kernel &
initramfs to have quicker boot times than uncompressed. I suspect the
default kernel boot may be optimized for relatively slow disk copy and
very fast processors [typical desktop]. In such a configuration a
long unzip operation probably is faster than coping a bigger image from
a slow disk.
Assuming there is a problem here, I have started to debug this.
basically gunzip() calls inflate(). After a few more calls we get to
inflate_codes() which ultimate ends in a call to memcpy(). What I have
observed and find very strange is that memcpy() is being used to
repeatedly copy a very small number of bytes (typically 1 to 4).
Occasionally it is called to copy a larger # of bytes. There are
literally tens (or hundreds) of thousands of memcpy to move a few MB
data. I suspect this is where the vast majority of the time is being
Is it possible that I am seeing an architecture specific problem?
Any comments/suggestions are welcome.
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