SD card performace ?
koenig at tat.physik.uni-tuebingen.de
Mon Aug 4 10:54:37 CEST 2008
some questions about SD card performace, right now running
# cat /proc/version
Linux version 2.6.24 (oe at buildhost.openmoko.org) (gcc version 4.1.2) #1 PREEMPT Wed Jul 30 11:56:48 CEST 2008
but with older (pre-GPS-fix) kernel I've seen similar read performace (haven't
looked at write performace before the GPS-fix.
a) read performace
in my gta02v5 I get ~3.2 MB/sec sustained read performace with the
shipped 512 MB sandisk card using e.g.
dd_rescue /dev/mmcblk0 /dev/null
when I do the same with this card in my Lenovo T61p (builtin sd card reader)
I get ~7.5 MB/sec. is there a chance to get better read performace ?
reading from /dev/mtdblock6 (the internal jffs2 partition?) I also get ~3.2 MB/sec
any chance to get better read performace (both for SD and the internal flash)?
what's the limiting factor ?
one term seems to be the block size (cp uses 4k I/O blocks):
# time dd if=/bin/bash of=/media/mmcblk0p2/bin/bash bs=4k
# time dd if=/bin/bash of=/media/mmcblk0p2/bin/bash bs=64k
# time dd if=/bin/bash of=/media/mmcblk0p2/bin/bash bs=1k
# time dd if=/bin/bash of=/media/mmcblk0p2/bin/bash bs=1b
is this really the max. cpu/system performace for a 400 MHz arm ?
talking about cpu performace: a first naiive read-test for /bin/bash
obviously was cpu bound (again, only ~1.4 MB/sec for 400 MHz?!):
# time wc -l /bin/bash
but dd shows reasonable read timing (cached):
# time dd if=/bin/bash of=/dev/null bs=4k
160+1 records in
160+1 records out
b) write performace
I just did a
# ls -l /bin/bash
-rwxr-xr-x 1 root root 659028 Jun 22 02:12 /bin/bash
# time cp /bin/bash /media/mmcblk0p2/bin/bash
and was surprised that this takes 3.9 to 4.2 seconds for _every_ run
(no caching effect for 2nd run). /bin/ is the internal flash jffs2,
/media/mmcblk0p2/ is ext3.
any comments (for performace fixes;-) ?
"I hope to die ___ _____
before I *have* to use Microsoft Word.", 0--,| /OOOOOOO\
Donald E. Knuth, 02-Oct-2001 in Tuebingen. <_/ / /OOOOOOOOOOO\
Harald Koenig // / \\ \
koenig at tat.physik.uni-tuebingen.de ^^^^^ ^^^^^
More information about the devel