There have been latencies of up to about ten seconds (no screen
refresh under X, no mouse movement) during writing large files (size
larger than RAM) to DVD-RAM under kernel 2.4.13 (also reported in
http://groups.google.com/groups?hl=en&selm=fa.dqbjqmv.1eh8lob%40ifi.uio.no
for kernel 2.4.0). These long latencies have gone with 2.4.17,
interactive work is now possible during writing to DVD-RAM on my
system. Excellent!
A performance problem still remains, however. Copying a large file
from HDD to DVD-RAM almost completely blocks a concurrent compilation
('make') process (which reads its input files from HDD, of course). To
illustrate the problem, here is an extract of 'vmstat 1' output. It's
continuous, I only copied the headers. Periods with almost no CPU
usage (and so no progress of the compilation process) alternate with
periods of high CPU and HDD usage. I consider this to be a performance
bug because the compilation process should be able to read (at least
some) data from HDD while data is written to DVD-RAM. Periods with low
CPU usage take much longer than those with high CPU usage.
# period with low CPU usage, high data rate written to DVD-RAM and
# no data read from HDD
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
0 3 2 31076 4488 5256 187248 0 0 0 3950 111 123 0 0 100
0 3 2 31076 4488 5256 187248 0 0 0 0 105 121 0 0 100
0 3 2 31076 4484 5256 187252 0 0 0 64 116 122 0 0 100
0 3 2 31076 4484 5256 187252 0 0 0 3872 111 122 0 0 100
0 3 2 31076 4484 5256 187252 0 0 0 0 113 123 0 0 100
0 3 2 31076 4484 5256 187252 0 0 0 0 111 118 0 1 99
0 3 2 31076 4484 5256 187252 0 0 0 4118 111 126 0 1 99
1 3 2 31076 4484 5256 187252 0 0 0 128 112 126 0 0 100
0 3 2 31076 4484 5256 187252 0 0 0 0 111 120 0 0 100
1 3 2 31076 4484 5256 187252 0 0 0 4080 113 127 0 1 99
1 3 2 31076 4484 5256 187252 0 0 0 0 114 297 1 0 99
1 3 2 31076 4476 5256 187256 0 0 0 64 111 414 5 0 95
0 3 2 31076 4472 5256 187256 0 0 0 0 106 700 6 1 93
0 3 2 31076 4472 5256 187256 0 0 0 0 106 130 0 0 100
2 2 2 31076 4460 5272 187300 0 0 4868 4028 207 370 0 9 91
0 3 2 31076 4424 5308 187304 0 0 8712 0 251 546 1 14 85
0 3 2 31076 4568 5320 187140 0 0 4998 0 196 371 0 9 91
# period with high CPU usage, almost no data written to DVD-RAM and
# high data rate from HDD
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
2 1 2 31076 11160 5352 186992 0 0 52 124 123 195 89 5 6
3 1 2 31076 12336 5352 187092 0 0 12 0 117 153 98 2 0
3 0 2 31076 7732 5352 187440 0 0 128 0 111 135 96 4 0
2 1 0 31460 7692 5324 193016 0 68 6932 68 221 404 85 15 0
3 0 0 31516 4432 5352 194652 0 444 7180 444 227 468 87 13 0
3 0 0 31516 4380 5380 190024 0 0 6668 0 208 522 91 9 0
2 1 0 31516 6236 5428 193832 0 0 6572 0 211 436 88 12 0
1 2 0 31516 4452 5452 195776 0 0 4834 0 192 380 73 13 14
3 0 0 31516 4368 5528 188876 0 0 6032 96 212 531 87 13 0
1 2 0 31516 10304 5468 188020 0 0 7436 0 219 512 83 17 0
3 0 0 31516 4356 5496 193052 0 0 6164 0 205 407 81 16 3
2 1 1 31516 4296 5488 188276 0 0 8584 0 233 571 91 9 0
3 0 0 31516 4856 5516 195472 0 0 6054 0 205 363 84 16 0
2 1 0 31516 4404 5500 189176 0 0 5764 104 204 494 89 11 0
2 1 0 31876 5180 5404 191620 0 332 6160 344 221 422 87 13 0
1 2 1 32016 4408 5432 194108 0 236 6064 8036 229 399 85 15 0
# a period with low CPU usage starts again
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
0 3 1 32016 4488 5436 193828 0 0 8 1386 128 137 6 1 93
0 3 1 32016 4488 5436 193828 0 0 0 3924 111 124 0 1 99
0 3 2 32016 4436 5488 193828 0 0 0 928 122 132 0 1 99
0 3 1 32016 4564 5488 193700 0 0 0 0 109 126 0 0 100
0 3 1 32016 4560 5488 193704 0 0 0 64 110 122 0 0 100
0 3 1 32016 4560 5488 193704 0 0 0 0 109 121 0 0 100
0 3 1 32016 4568 5492 193692 0 0 128 4082 116 136 0 3 97
1 3 1 32016 4568 5492 193692 0 0 0 0 116 127 0 0 100
0 3 2 32016 4536 5520 193692 0 0 0 554 118 130 0 0 100
2 1 2 32016 8440 5532 193260 0 0 2820 162 156 268 32 5 63
1 2 2 32016 4384 5496 192272 0 0 4496 5356 193 372 87 13 0
0 3 2 32016 4364 5496 191840 0 0 0 1260 112 133 71 0 29
The ATAPI DVD-RAM in on /dev/hdc, the HDD is on /dev/hda, so they
should be completely independent and processes should be able to
read/write to HDD and read/write to DVD-RAM at the same
time. Apparently, this is unfortunately not the case.
What's the reason for this misbehaviour of the kernel and what can be
done against it?
Thank you in advance,
Moritz
Here is some data of my system:
My system is SuSE 7.1.
Kernel is an original 2.4.17. (I have also
tried the preemptive kernel patch 'preempt-kernel-rml-2.4.17-1.patch'
but neither improves latencies of 2.4.13 nor does it improve the
behaviour of 2.4.17 described above.)
cat /proc/version
Linux version 2.4.17 (root@nomad) (gcc version 2.95.2 19991024 (release)) #1 Thu Dec 27 20:35:47 CET 2001
lsmod
Module Size Used by
nls_iso8859-1 2880 0 (autoclean)
nls_cp437 4384 0 (autoclean)
ide-floppy 11360 0 (autoclean)
tuner 8160 1 (autoclean)
tvaudio 9840 0 (autoclean) (unused)
msp3400 14160 1 (autoclean)
bttv 60624 0 (autoclean)
i2c-algo-bit 7168 1 (autoclean) [bttv]
i2c-core 12944 0 (autoclean) [tuner tvaudio msp3400 bttv i2c-algo-bit]
videodev 4640 3 (autoclean) [bttv]
vfat 9520 0 (autoclean)
fat 29728 0 (autoclean) [vfat]
ide-cd 26672 1 (autoclean)
cdrom 28928 0 (autoclean) [ide-cd]
es1371 27072 1 (autoclean)
soundcore 3568 4 (autoclean) [es1371]
ac97_codec 9680 0 (autoclean) [es1371]
mga 103456 1
agpgart 26320 1 (autoclean)
autofs4 8576 2 (autoclean)
ne2k-pci 5056 1 (autoclean)
8390 6032 0 (autoclean) [ne2k-pci]
apm 9168 1
mount
/dev/hda3 on / type reiserfs (rw,noatime)
proc on /proc type proc (rw)
devpts on /dev/pts type devpts (rw,mode=0620,gid=5)
/dev/hda1 on /boot type ext2 (rw,noatime)
/dev/hda6 on /home type ext2 (rw,noatime)
/dev/hda7 on /lscratch type reiserfs (rw,noatime)
shmfs on /dev/shm type shm (rw)
automount(pid332) on /net type autofs (rw,fd=5,pgrp=332,minproto=2,maxproto=4)
automount(pid330) on /misc type autofs (rw,fd=5,pgrp=330,minproto=2,maxproto=4)
/dev/hdc on /dvd type ext2 (rw,noexec,nosuid,nodev,user=jfranosc)
cat /proc/ide/ide1/hdc/driver
ide-cdrom version 4.59
cat /proc/ide/ide1/hdc/model
TOSHIBA DVD-RAM SD-W2002
cat /proc/ide/ide1/hdc/capacity
8946816
cat /proc/ide/ide1/hdc/settings
name value min max mode
---- ----- --- --- ----
breada_readahead 4 0 127 rw
current_speed 34 0 69 rw
dsc_overlap 0 0 1 rw
file_readahead 0 0 2097151 rw
ide_scsi 0 0 1 rw
init_speed 12 0 69 rw
io_32bit 1 0 3 rw
keepsettings 0 0 1 rw
max_kb_per_request 127 1 127 rw
nice1 1 0 1 rw
number 2 0 3 rw
pio_mode write-only 0 255 w
slow 0 0 1 rw
unmaskirq 1 0 1 rw
using_dma 1 0 1 rw
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