[linux-cifs-client] poor cifs write performance and high CPU load with large files (500MB+) compared to smbfs

[Martin Koeppe]

Hello list,

I first wrote about this issue to the Debian Bug tracking system, see:
http://bugs.debian.org/309405
but was then redirected to this list:

I run a Linux box with Debian Sarge within a VMware, a Windows Server 2003
and a Windows 2000 Server (both not in VMware). When copying a CD image file
from within Linux to a cifs mounted Win2003 share, I see a very poor
performance and high CPU load (about 90% system) on the Linux VM. Copying
begins with 3 MB/s (measured by mc), after 4% (this varies) it suddenly
stops for say 10-20 seconds, then continues with 1..2 MB/s, but stopping
from time to time for several seconds. CPU load is only high while copying,
not in the pauses. Copying the whole file (700MB) took about 10 minutes.

Copying the same file in the same direction from a samba share at the W2K3
box is very much faster, copying is finished in about a minute, and CPU load
on the Linux side is by far less.

Also, reading from the cifs mounted share (and thus copying from W2K3 to
Linux) is by far faster (8MB/s).

When copying the same file from Linux to a cifs mounted Windows 2000 share,
I get a similar picture: Copying begins with 3 MB/s, but soon slows down to
1 MB/s with high CPU load. But here, it doesn't seem to have these long idle
times. Nevertheless copying takes about 10 minutes, too.

When mounting the Win2000 share with smbfs and writing to that, however, I
get about 4 MB/s and a system load of approx. 35%.


I don't think it has anything to do with VMware as all other transfers
from and to this Linux VM are fast (NFS, HTTP, FTP, and Samba as mentioned).
(FTP and NFS copy performs with 10 MB/s)

I tried to compile a new kernel with the newest CIFS (1.34), but
unfortunately it doesn't compile with the Debian sarge kernel sources for
2.6.8, neither plain 1.34 nor 1.34-RHEL4.

CIFS 1.34 does compile with Debian sid kernel 2.6.11, but unfortunately, the
VMware net driver doesn't work with this kernel, so I cannot test this.

I cannot test smbfs with W2K3 for comparison either, as I don't want to
modify the W2K3 settings to allow non-signed SMB.

On the Linux side I could test nearly everything, however, if somebody has
some more ideas what to test.


Martin