Welcome Lenny

Just did an aptitude dist-upgrade to get planet.classpath.org and the main IcedTea backup server from Debian Etch to Debian Lenny. Pretty smooth.

Needed to adjust some apache2 NameVirtualHost settings as outlined in the release notes. And sadly, had to pin mercurial to 0.9.5, since newer versions don’t work nicely with the forest extension and serving hg through http hgwebdir. But that was it. Everything else went without any hiccups.

But if you use one of those servers and do notice something wrong, please let me know.

Syndicated 2009-03-01 20:50:57 from Mark J. Wielaard

Systemtap 0.9 - Cast away

Another nice feature for Systemtap 0.9 was added by Josh Stone. Systemtap can collect data from any variable in scope at a probe point using the DWARF debug info. You can even dereference pointers, access struct members, array elements, etc. This is very powerful when collecting data during a trace and the systemtap runtime makes sure all data access is safe. But there were two issues making this less powerful than it could be.

First to the keep the tracing language simple systemtap only supports basic types (integers and strings), associative arrays or aggregates in stap scripts. This means that you could not easily pass program data around to an helper function to manipulate or format. Second sometimes programs “hide” the real type of a variable, or use a void * pointer that gets cast to the right type later on. You could work around this in the past by using embedded C and guru mode, but that wasn’t very nice, and made your script potentially unsafe.

So to make sure you can do this safely Josh added a @cast construct. This allows you to pass around a pointer to program data and interpret it as if it was any type described in the DWARF debuginfo for the program. All accesses are of course still checked for safety by the runtime.

A nice example of this feature in action is the following simple stap script to print the number of incoming connections for an executable by port number. We want to probe the kernel and get the inet_sock from the inet_csk_accept function when it returns successfully. Although this function handles inet sockets (it is part of inet_connection_sock.c), it passes around sock pointers. It can do this since an inet_sock struct starts with a sock pointer, later it will cast this to a full featured inet_sock pointer. So we do the same in our script:

global ports;

probe kernel.function("inet_csk_accept").return
{
  sock = $return
  if (sock != 0)
    {
      port = @cast(sock, "inet_sock")->num;
      ports[execname(), port]++;
    }
}

probe timer.s(30), end
{
  printf("Connections on ports: %s\n", ctime(gettimeofday_s()));
  foreach ([exec, port] in ports-)
    printf("%12s %4d: %4d\n", exec, port, ports[exec, port]);
  delete ports;
}

</blockquote

$ stap ports.stp
Connections on ports: Sat Feb 28 22:49:10 2009
       httpd   80:   10
        exim   25:    6
       spamd  783:    4
  imap-login  993:    2
        sshd   22:    2

There are some more elaborate network tracing examples in the Systemtap Examples collection.

Syndicated 2009-02-28 23:07:43 from Mark J. Wielaard

Systemtap 0.9 - Markers everywhere

We recently released Systemtap 0.9 and one of the nice new features included is the user space markers that Stan Cox has been working on. They were designed so that they should be compatible with dtrace static user space markers, so you can immediately take advantage of them if your program already has those included. It even comes with a little dtrace python script wrapper that automagically does the right thing during the build. A nice example of that is postgresql, which has a set of markers to observe transactions, database locks, etc. All you have to do is recompile postgresql with –enable-dtrace and tada, out roll systemtap enabled markers that you can use for getting some high level events from your database. Like for example how many and how long transactions take:

$ stap -x `pgrep -n postgres` postgresql-transactions.stp
committed transactions:
transaction id: time
            34: 1593213ns
            36: 2817146ns
            37: 1463901ns
            38: 1427854ns

aborted transactions: 4

We are trying to get some of these static markers activated in packages compiled for Fedora as SystemtapStaticProbes F11 Feature, so you can use them out of the box.

But you can also add your own markers to existing code. Daniel Tralamazza has been experimenting with a small glibc patch to add markers around various pthread mutexes, for doing userland synchronization primitives analysis. Then you can easily get things like the top 10 most shared locks.

Syndicated 2009-02-24 15:41:48 from Mark J. Wielaard

Some Fosdem pictures

Sarah has been publishing sets of pictures from the Fosdem Free Java Meeting. <tbody> </tbody>

Syndicated 2009-02-11 07:53:38 from Mark J. Wielaard

IcedTea 1.4 with XRender support

IcedTea 1.4 got released this week. And while it is full of new exciting stuff, you really should check out the XRender support by Clemens Eisserer. Especially if you often use java through remote X. It just flies! Trying it out is easy as soon as the new IcedTea hits a distro near you:

java -Dsun.java2d.xrender=True my.fancy.gui.HelloWorld

Also check out the JGears2 benchmark to compare your results.

So this speeds up the rendering pipeline to X enormously. Now the next step will be optimizing or rewriting the actual Render backend (pisces at this time) which seems to be the next bottleneck, at least for anti-aliased operations.

Clemens will give a talk about his work at Fosdem. Hope to see you all there.

Syndicated 2009-02-05 08:51:16 from Mark J. Wielaard