Gino Ruopolo wrote:
When I get a chance, I'll reproduce many
connections/s (instead of
bytes/s) across zones, compared to intra-zone, using
Apache's 'ab'
tool, and report what I get. -- Jeff
that would be very similar to my setup.
thankyou
gino
This message posted from opensolaris.org
As promised, I've done some tests on the scenario Gino described: higher
CPU overhead for a workload containing many connections per second when
client and server processes are in different zones than when in the same
zone. Sorry for the delay, but besides other activities getting in the
way, I wanted to conduct good tests where I had a reasonable degree of
confidence that I was correctly measuring the right thing. My apologies
for the long e-mail - send to bit bucket if it's too much detail :-)
I tested with Nevada build 55 (perhaps I would get different numbers on
stock Solaris 10, so maybe I'll retry this next week on a machine
running S10), with most tests done on a fairly old PC (Pentium III at
1Ghz). I created zones named zone1 and zone2 (very creative, I know...),
and configured Apache 2. For workload, I used the Apache benchmark tool
('ab'), and the http_load from Acme.com. In each test, I fetched the
same URL, pointing to static HTML, in order to eliminate variable
overhead from dynamic content and/or disk I/O.
Many thousands of web hits later and multiple runs with an otherwise
idle box, I measured an average 692.82 hits per second when both
http_load and httpd were in the same zone, and 679.27 going from zone2
to zone1. That's a ratio of 0.9804, so inter-zone results were 98.04% of
the rate of same-zone traffic. Normally I'd be inclined to consider
under 2% difference "noise", but the results over multiple trials (and
also when using 'ab' instead of http_load) seemed consistent: a small
difference in the same direction.
I then used DTrace to see where I was spending time, both elapsed and
CPU time (timestamp and vtimestamp) and got the following results (shown
is output from same-zone traffic) for the most dominant system calls:
vtime by function
httpd
writev 71642973
httpd
accept 71720121
httpd
shutdown 76473328
http_load
close 89913014
http_load
connect 149196319
elapsed time by function
httpd
writev 85014366
httpd
shutdown 90492746
http_load
close 102127944
http_load
connect 162967191
httpd
accept 17908653425
total vtime by execname: http_load 351417154, httpd 434824250
total wall time by execname: http_load 456124949; httpd 18503892793
The actual times aren't of consequence: what is significant is where
time was spent (the same system calls consistently appeared in both
same-zone and different-zone cases), and the different between same-zone
and different zone tests. I measured CPU time slightly higher in the
different-zone case: 5.76% higher for client (http_load), and 2.04%
higher for Apache httpd. So pending further investigation, it does seem
there is a small difference in time when an application with many
connections per second is in the same zone compared to different zones.
This does not explain the issues Gino raised in his original post, where
he reported a bigger change in performance. It does not seem to be
related to the cost of network connections, and we have a few ideas on
where they may be. We've corresponded privately, and I've sent him some
DTrace scripts, so we will pursue this further together. Thank goodness
for DTrace!
cheers, Jeff
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