A tricky question to answer.
On ARM based Zaurus handhelds the kernel has to fit into a 1.2MB
partition. It makes sense to have as much core functionality compiled
into the kernel as possible but its becoming increasingly difficult to
fit functional kernels into the space available. The devices only have
32MB or 64MB of RAM so a small kernel runtime is also a priority.
I wanted to compare a 2.6.17 build with 2.6.23 but comparing kernels is
surprisingly difficult. scripts/bloat-o-meter tells me about the
differences in function size but lots of functions were renamed and
between .17 and .23 the results are nearly meaningless.
The information below is a summary of the quick hacks I used to find out
where the size change (bloat?) was coming from. I'm mentioning it here
since some of the results are interesting and I'm also hoping someone
with more time might be able to improve the script and/or this way of
analysing the kernel...
To look at my specific problem I hacked "bloat-by-subsys" together
(included below). It only cares about the things built into the kernel,
specifically by looking at the "built-in.o" files as I wanted to look at
the "core". It assumes the tree layout didn't change too much between
the two kernel versions (directories move a lot less frequently than
function names change) and that directories make good units for
comparison.
The output from two kernel trees for the poodle machine I happened to
have handy was:
function old new delta
./kernel/built-in.o 203261 326552 +123291
./drivers/built-in.o 496936 616632 +119696
./kernel/time/built-in.o - 67028 +67028
./drivers/video/built-in.o 91772 131002 +39230
./drivers/video/logo/built-in.o 4104 38002 +33898
./drivers/hid/built-in.o - 24970 +24970
./kernel/irq/built-in.o - 23668 +23668
./drivers/cpufreq/built-in.o - 21910 +21910
./fs/built-in.o 436077 457252 +21175
./drivers/mmc/core/built-in.o - 16724 +16724
./net/built-in.o 479570 493951 +14381
./arch/arm/mach-pxa/built-in.o 12336 24284 +11948
./drivers/mmc/built-in.o 15712 25972 +10260
./mm/built-in.o 143359 153248 +9889
./net/ipv4/built-in.o 252918 261638 +8720
./drivers/base/built-in.o 30892 39160 +8268
./drivers/char/built-in.o 117976 125357 +7381
./net/core/built-in.o 105436 112412 +6976
./drivers/mmc/card/built-in.o - 5880 +5880
./arch/arm/common/built-in.o 11076 16172 +5096
./net/wireless/built-in.o - 4728 +4728
./drivers/input/built-in.o 17008 21132 +4124
./crypto/built-in.o 7992 12008 +4016
./fs/proc/built-in.o 34544 38512 +3968
./drivers/mmc/host/built-in.o - 3368 +3368
./lib/built-in.o 32112 35424 +3312
./net/netlink/built-in.o 18062 21070 +3008
./lib/lzo/built-in.o - 2880 +2880
./ipc/built-in.o 19388 22064 +2676
./drivers/video/console/built-in.o 47773 50009 +2236
./drivers/input/touchscreen/built-in.o 0 2104 +2104
./fs/sysfs/built-in.o 12960 14936 +1976
./drivers/pcmcia/built-in.o 41300 43244 +1944
./arch/arm/mm/built-in.o 17584 19000 +1416
./fs/jffs2/built-in.o 79280 80344 +1064
./net/netfilter/built-in.o 8548 9276 +728
./net/unix/built-in.o 16864 17489 +625
./net/ipv6/built-in.o 3980 4596 +616
./drivers/serial/built-in.o 18356 18952 +596
./kernel/power/built-in.o 3048 3632 +584
./fs/partitions/built-in.o 4272 4824 +552
./drivers/ide/built-in.o 68017 68529 +512
./drivers/ide/legacy/built-in.o 3988 4404 +416
./drivers/block/built-in.o 8280 8696 +416
./drivers/leds/built-in.o 4736 4984 +248
./drivers/usb/gadget/built-in.o 9232 9412 +180
./drivers/rtc/built-in.o 10892 11064 +172
./block/built-in.o 47218 47366 +148
./drivers/input/keyboard/built-in.o 1396 1508 +112
./net/packet/built-in.o 11240 11308 +68
./net/ethernet/built-in.o 1187 1247 +60
./fs/fat/built-in.o 30750 30806 +56
./arch/arm/nwfpe/built-in.o 23697 23737 +40
./security/built-in.o 1548 1544 -4
./drivers/mtd/maps/built-in.o 796 792 -4
./fs/devpts/built-in.o 1556 1540 -16
./fs/vfat/built-in.o 6592 6516 -76
./drivers/net/built-in.o 1668 1580 -88
./drivers/video/backlight/built-in.o 3016 2900 -116
./fs/nls/built-in.o 9656 9536 -120
./lib/zlib_deflate/built-in.o 17536 17412 -124
./drivers/mtd/chips/built-in.o 1272 1036 -236
./drivers/mtd/built-in.o 44938 44694 -244
./fs/ramfs/built-in.o 1560 1300 -260
./drivers/mtd/nand/built-in.o 24864 24504 -360
./fs/ext2/built-in.o 27692 27260 -432
./drivers/i2c/busses/built-in.o 3428 2960 -468
./drivers/i2c/built-in.o 16037 15490 -547
./net/sched/built-in.o 4284 3656 -628
./drivers/base/power/built-in.o 3328 2220 -1108
./drivers/i2c/algos/built-in.o 4697 2786 -1911
./lib/zlib_inflate/built-in.o 11452 8920 -2532
./init/built-in.o 19803 9412 -10391
./net/xfrm/built-in.o 45808 35132 -10676
./arch/arm/kernel/built-in.o 45613 30028 -15585
Some information is repeated here as a high level built-in.o contains
the built-in files from the directories below it. I think this
simplistic approach provides a good overview of the status though.
The single most shocking figure is that for ./kernel which showed a 60%
increase in size:
./kernel/built-in.o 203261 326552 +123291
./kernel/time/built-in.o - 67028 +67028
./kernel/irq/built-in.o - 23668 +23668
./kernel/power/built-in.o 3048 3632 +584
I've not looked into it yet but it makes me wonder what I gained for the
123kb of RAM usage and the increased kernel size... (yes, from the above
I can make some guesses)
The results also highlight other issues, I've given interpretations of
some of the changes below:
function old new delta
./drivers/video/logo/built-in.o 4104 38002 +33898
A logo was added into the 2.6.23 defconfig, this highlights the space it
takes up...
./drivers/hid/built-in.o - 24970 +24970
This shouldn't be being built in, a defconfig error
./drivers/cpufreq/built-in.o - 21910 +21910
2.6.17 didn't have cpufreq support
./arch/arm/mach-pxa/built-in.o 12336 24284 +11948
Probably from the pxa updates to support multiple cpus and the pxa3xx
series in one kernel - it comes at a price.
./lib/lzo/built-in.o - 2880 +2880
LZO wasn't present in 2.6.17
./drivers/input/built-in.o 17008 21132 +4124
./drivers/input/touchscreen/built-in.o 0 2104 +2104
I disabled the touchscreen in 2.6.17 due to build issues so this is
partly bogus. This was the only change I made to the code.
./arch/arm/nwfpe/built-in.o 23697 23737 +40
Probably the NWFPE preempt fixes.
./drivers/video/backlight/built-in.o 3016 2900 -116
Probably the backlight cleanup.
./lib/zlib_deflate/built-in.o 17536 17412 -124
./lib/zlib_inflate/built-in.o 11452 8920 -2532
The zlib update had the side effect of space savings!
./fs/ext2/built-in.o 27692 27260 -432
I didn't expect that...
./net/xfrm/built-in.o 45808 35132 -10676
./net increased overall in size though counteracting this quite a bit...
./init/built-in.o 19803 9412 -10391
./arch/arm/kernel/built-in.o 45613 30028 -15585
Some good looking code size changes here at least at first glance.
So some of the changes were due to extra features, one was an accidental
defconfig misconfiguration. There were surprise space savings and some
worrying size increases.
The script itself, keep in mind this is an extremely quick hack and it
could be a ton more efficient. Certain code was left in case I wanted to
go back to looking at things at a function level too:
#!/usr/bin/python
#
# Copyright 2007 Richard Purdie <[email protected]>
# Copyright 2004 Matt Mackall <[email protected]>
#
# Based on python Bloat-O-Meter (c) 2004 by Matt Mackall
#
# This software may be used and distributed according to the terms
# of the GNU General Public License, incorporated herein by reference.
import sys, os, re
if len(sys.argv) != 3:
sys.stderr.write("usage: %s tree1 tree2\n" % sys.argv[0])
sys.exit(-1)
def getsizes(file):
sym = {}
total = 0
for l in os.popen("nm --size-sort " + file).readlines():
size, type, name = l[:-1].split()
if type in "tTdDbB":
if "." in name: name = "static." + name.split(".")[0]
sym[name] = sym.get(name, 0) + int(size, 16)
total = total + sym[name]
return sym, total
startdir = os.getcwd()
old = {}
total_old = {}
os.chdir(sys.argv[1])
for root, dirs, files in os.walk("."):
for name in files:
if name == "built-in.o":
fn = os.path.join(root, name)
old[fn], total_old[fn] = getsizes(fn)
os.chdir(startdir)
new = {}
total_new = {}
os.chdir(sys.argv[2])
for root, dirs, files in os.walk("."):
for name in files:
if name == "built-in.o":
fn = os.path.join(root, name)
new[fn], total_new[fn] = getsizes(fn)
os.chdir(startdir)
grow, shrink, add, remove, up, down = 0, 0, 0, 0, 0, 0
delta, common = [], {}
for a in total_old:
if a in total_new:
common[a] = 1
for name in total_old:
if name not in common:
remove += 1
down += total_old[name]
delta.append((-total_old[name], name))
for name in total_new:
if name not in common:
add += 1
up += total_new[name]
delta.append((total_new[name], name))
for name in common:
d = total_new.get(name, 0) - total_old.get(name, 0)
if d>0: grow, up = grow+1, up+d
if d<0: shrink, down = shrink+1, down-d
delta.append((d, name))
delta.sort()
delta.reverse()
print "%-40s %7s %7s %+7s" % ("function", "old", "new", "delta")
for d, n in delta:
if d: print "%-40s %7s %7s %+7d" % (n, total_old.get(n,"-"), total_new.get(n,"-"), d)
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