Name: boT120536 Date: 02/19/2001


java version "1.3.0"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0)
Java HotSpot(TM) Client VM (build 1.3.0, mixed mode)


We performed some benchmarks at the Sun Benchmark Center in Langen/Germany. The
tests were perfomed on a E6500 with 30 336MHz CPUs. We saw, that there was a lot
of sys-time consumed by the JRE itself.

The following information applies to a Java program like the following. The
result is independent of -hotspot, -client or -server.
public class test {
public static void main(String args[]) throws Throwable {
Object o=new Object();
synchronized (o) { o.wait(); }
}
}

1. the JRE goes into a poll(?,0,10) endless loop. That consumes about .25
CPU-seconds in about 5 seconds (says truss) on a 30 CPU machine. On a single CPU
machine that loop consumes about .00 CPU-seconds.

2. SIGALRM is received every second and interrupts every lwp_sema_wait. The more
threads are waiting e.g. on a java.lang.Object.wait(), the more CPU time is
consumed.

For example: A process with ~35 threads does about 200 system calls per second.
Isn't that too much? Even on a single CPU system this process consumes .03s
doing effectivly nothing.

Sample (from "truss -c -p n"):
---------------------------------------------------------------------------
signals ------------
SIGALRM 16
total: 16

syscall seconds calls errors
poll .00 214
sigprocmask .03 54
context .01 16
lwp_sema_wai .00 50 15
lwp_sema_pos .01 35
setitimer .00 31
lwp_mutex_un .04 35
lwp_mutex_lo .00 35
                ---- --- ---
sys totals: .09 470 15
usr time: .00
elapsed: 2.30
---------------------------------------------------------------------------

On the E6500 w/30 CPUs we saw, that a lot of time, a java process consumes, is
spent for (in my opinion unnecessary) system calls. About 10-250 times more time
is spent for system calls than real user time (including what's caused by
synchronized statements). It's not really nice to see a big machine spending its
expensive CPUs for a lot of system calls.
(Review ID: 117259)
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