#26 Very low transfer speed under 2.6 kernels

[Ciprian Popovici]

I'm getting very low transfer speeds when copying files to and from USB devices mounted via supermount. The problem appears only for USB devices (ie. not for CD's or DVD's), only when I mount them in read/write mode (ie. not when mounted read-only) and only for supermount. The problem does not appear if I mount them directly. This happens for a wide range of USB devices: card readers, HDD's in USB racks, flash sticks, with either FAT or ext3 filesystems on them.

Here's an example of how I use supermount:

mount -t supermount -o \
fs=vfat,dev=/dev/sda1,--,rw,uid=0,gid=100,umask=0007 \
none /mnt/usb/sda/1st

The latest kernel I've tried is vanilla 2.6.20, with supermount as the only patch.

I'm attaching the kernel configuration. If I can help by activating debugging on supermount please let me know what flags to use.

[Ciprian Popovici]

2.6.20 config

[Ciprian Popovici]

Logged In: YES
user_id=667423
Originator: YES

One more thing: it consumes 100% CPU while copying. According to /proc/stat and various monitors, the cpu spends most time doing system calls, not user, not I/O.