More benchmarking - openssl speed

Lluís Batlle i Rossell viriketo at gmail.com
Tue Dec 7 12:18:23 EST 2010


Hello back,

On Sat, Dec 04, 2010 at 11:30:39PM +0100, Lluís Batlle i Rossell wrote:
> I attach the results I got in the nanonote, having openssl 1.0.0b built with gcc
> 4.5.1 (for a generic 32-bit system).
> 
> Notice that the time measures at the last part of the benchmark get to 0.0s; I
> have no idea why this happens.

I investigated the problem a bit. 'stracing', I saw that openssl uses the
"times()" system call to get the user-mode time spent since it started the work
and a SIGALRM came programmed by alarm(3).

For usual cases, as openssl moves mainly user-mode code (cipher-related
algorithms), the user-mode time difference should be around 3 seconds.

strace showed that in the kernel I was using (2.6.35 openwrt trunk)
times() reported an increasing user-time during the first ~11 minutes, and the
kernel-mode time increased only a little (mainly due to writes to the terminal I
imagine, and the other few syscalls like alarm/times involved).
After ~11 minutes (around 64k jiffies), the user-time stalled, and all the
jiffies got added into the kernel-mode jiffie counter.

The value at which the user-time stalled was different at every run, but always
around 64k.

I could reproduce the problem also with gzip looking at the jiffie counters at
/proc/PID/stat. So it was not related to openssl.

barbes on irc checked the 2.6.32.10 qi-openwrt kernel, and he could not
reproduce the problem.

I built and run the 2.6.36 openwrt-trunk kernel, and there I also could not
reproduce the trouble.

And that is all I tested.

So I leave it as a bug only in 2.6.35.

Regards,
Lluís.




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