-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 08/03/10 15:47, James Yonan wrote: > I believe this has been discussed before, but I noticed recently that a > Linux-based OpenVPN client (Linux 2.6.24, OpenVPN 2.1.1) spends a lot > more CPU time in kernel space than in user space. This is surprising, > given the fact that all of the CPU-intensive cryptographic operations > are being done in user space. > > Using the 'time' utility on the OpenVPN client, while a wget of a 50MB > file was done over the VPN, I found that 80% of the CPU time was taken > by the kernel, and 20% by user space (I should add that the Linux client > was running as a VM on VMWare Fusion). > > I'm wondering if anyone with kernel background has any insights on this. > Are there performance bottlenecks in the tun/tap driver?
I'm not a hardcore kernel developer, but I'm interested in the to James, would you mind trying to run a test on the 2.6.33 kernel? That's the newest stable kernel available, just to see if your observations are visible there as well, and if they are better or worse. And when you say earlier kernels did not use so much time in kernel space, which kernels did you compare against? It would be interesting to look through the changelog from the "good" kernel version to 2.6.24, to see what was changed in tun.c. In this case, it would be easier to try to nail down where such a behavioural change happened. And after all, 2.6.24 was released about 2 years ago (Jan 24 14:58:37 2008) ... and the drivers/net/tun.c has been changed 72 times, as far as I can see. It's a big job going on getting rid of the BKL (big kernel lock, blocking all apps while kernel is doing something) ... so it's difficult to say now just what could have been the reason for what you observe. James, if you have a "test script" with configuration files, I can setup a test environment and run some tests and also enable ftrace [1], which could also pin-point more where the kernel spends its time doing things. kind regards, David Sommerseth [1] <http://www.wireshark.org/lists/wireshark-dev/200911/msg00260.html> [ --------- For the curious mind - checking changelog for a specific file in the kernel tree: * git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git * cd linux-2.6 * only commit messages: git log --follow v2.6.24..v2.6.33 -- drivers/net/tun.c * with full diff: git log -p --follow v2.6.24..v2.6.33 -- drivers/net/tun.c ---------- ] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org/ iEYEARECAAYFAkuWS+kACgkQDC186MBRfroKbwCdE5hVcQGREOaa7P+eASb6FVmC 9usAmgIYhhykLsIf6NPpe1os8kk1tTsq =qlB9 -----END PGP SIGNATURE-----
