Tuesday, September 13, 2011

Storage Speed on the PandaBoard Revisited (Again)

Since my last post, I took a short vacation and I've been helping in the Virtual Fedora Activity Days (VFAD) to rebuild packages for Fedora 15 hardfp (hardware floating point).

Research into the slow storage speeds on the PandaBoard (and other Cortex-ARM9 systems) has continued and a patch set developed to hopefully improve the situation.  David Marlin built a kernel with the patch set, so I downloaded a copy and ran bonnie++ again.

The results were mixed for the SD card.  Sequential reads had a nice improvement, but sequential output and random seeks took a big hit.  The random seek times are particularly worrisome with an increase from 663ms to 76023ms!  Something doesn't seem right.

The USB hard drive, though, saw some nice improvements overall. Sequential write latencies dropped from 5.8 seconds down to 0.38 seconds and throughput more than doubled: 9 MiB/s vs 23 MiB/s!  Sequential reads latencies increased a bit, but throughput again more than doubled: 12 MiB/s vs 27 MiB/s!  Random seeks also saw a nice improvement from 7.6s down to 4.9s.

Version 1.96Sequential OutputSequential InputRandom
SizePer CharBlockRewritePer CharBlock
K/sec% CPUK/sec% CPUK/sec% CPUK/sec% CPUK/sec% CPU/sec% CPU
SD Card 2.6.35-g6d019da-dirty2G4193312553371433699175981527.41
SD Card
USB HD 2.6.35-g6d019da-dirty2G4399901716453863699912357993.96

I also tried a simple test with hdparm as shown on lwn.net:

[root@fedora-arm ~]# uname -r

[root@fedora-arm ~]# hdparm -t /dev/mmcblk0p4

 Timing buffered disk reads:   50 MB in  3.10 seconds =  16.11 MB/sec

[root@fedora-arm ~]# hdparm -t /dev/sda1

 Timing buffered disk reads:   66 MB in  3.05 seconds =  21.64 MB/sec

Compared to the older kerrnel:

[root@fedora-arm ~]# uname -r

[root@fedora-arm ~]# hdparm -t /dev/mmcblk0p4

 Timing buffered disk reads:   50 MB in  3.09 seconds =  16.20 MB/sec

[root@fedora-arm ~]# hdparm -t /dev/sda1

 Timing buffered disk reads:   26 MB in  3.04 seconds =   8.56 MB/sec

The SD card's performance is about the same, but the USB hard drive is much faster with the new patch!


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  2. Your results show the performance of USB_interface+hard_disk versus MMC_interface+SD_flash. It would be interesting to also see the results of testing a USB flash drive, to try and establish the performance difference at the actual transfer protocol layer (USB vs MMC).