--bwlimit - writing vs reading performance

[Pei Ku]

# Environment (both local and remote hosts):

$ /usr/bin/rsync --version
rsync  version 2.5.7  protocol version 26
Copyright (C) 1996-2002 by Andrew Tridgell and others
<http://rsync.samba.org/>
Capabilities: 64-bit files, socketpairs, hard links, symlinks, batchfiles,
              IPv6, 64-bit system inums, 64-bit internal inums

$ uname -a
Linux dbrac-01 2.4.9-e.27enterprise #1 SMP Tue Aug 5 15:39:21 EDT 2003 i686 unknown



# Tests Cases (local machine is 'dbrac-01'; remote machine is 'dbrac-02'):


$ rsh dbrac-02 rm xxx; /usr/bin/rsync -v --rsync-path=/usr/bin/rsync xxx dbrac-02:`pwd`/
xxx
wrote 11134869 bytes  read 36 bytes  7423270.00 bytes/sec
total size is 11133439  speedup is 1.00

$ rm xxx; /usr/bin/rsync -v --rsync-path=/usr/bin/rsync dbrac-02:`pwd`/xxx .
xxx
wrote 32 bytes  read 11134873 bytes  7423270.00 bytes/sec
total size is 11133439  speedup is 1.00

# write-to and read-from tests both yield throughput about 7.4 MB/s



$ rsh dbrac-02 rm xxx; /usr/bin/rsync -v --rsync-path=/usr/bin/rsync --bwlimit=8000 xxx dbrac-02:`pwd`/
xxx
wrote 11134869 bytes  read 36 bytes  2474423.33 bytes/sec
total size is 11133439  speedup is 1.00

# 2.4 MB/s is a lot less than specified bwlimit (8.0 MB/s)

$ rm xxx; /usr/bin/rsync -v --rsync-path=/usr/bin/rsync  --bwlimit=8000  dbrac-02:`pwd`/xxx .
xxx
wrote 32 bytes  read 11134873 bytes  404905.64 bytes/sec
total size is 11133439  speedup is 1.00

# at bwlimit of 8000 KB/s, write-to performance is 2.4 MB/s; read-from: 0.4 MB/s


$ rsh dbrac-02 rm xxx; /usr/bin/rsync -v --rsync-path=/usr/bin/rsync --bwlimit=16000 xxx dbrac-02:`pwd`/
xxx
wrote 11134869 bytes  read 36 bytes  3181401.43 bytes/sec
total size is 11133439  speedup is 1.00

# 3.2 MB/s is a lot less than specified bwlimit (16.0 MB/s)

$ rm xxx; /usr/bin/rsync -v --rsync-path=/usr/bin/rsync  --bwlimit=16000  dbrac-02:`pwd`/xxx .
xxx
wrote 32 bytes  read 11134873 bytes  390698.42 bytes/sec
total size is 11133439  speedup is 1.00

# at bwlimit of 10000 KB/s, write-to performance is 3.2 MB/s; read-from: still 0.4 MB/s



Questions:

- in the write-from-local-to-remote cases, the actual throughput does not correspond to 
the specified bwlimit.  But at least the actual throughput increases as the specified 
bwlimit increases

- in the read-from-remote-to-local case, changes in bwlimit has no impact on the actual
throughput.  And the actual throughtput is a lot less than the case when bwlimit is
not specified (0.4 MB/s vs. 7.4 MB/s)


bug in bwlimit implementation?


thanks



Pei L. Ku