About performance of D-Bus

[Jerome Philbert]

Thanks again for your analysis, Havoc.

Finally, your suggestions for optimizing speed, consist in removing security
and check from DBus, what is contrary to the interest of D-Bus, especially
if it is designed for an open platform.
But I cannot have both speed and security :-)

I think I have also tried your suggestions number 3 and 4.
Is not it equivalent to:
- remove paranoid validation ? (by using
DBUS_VALIDATION_MODE_WE_TRUST_THIS_DATA_ABSOLUTELY in the code)
- build D-Bus with disable-checks option ?
In this way, I have measured that D-Bus was 7% faster.

Jerome


2008/11/4 Havoc Pennington <hp at pobox.com>

> Hi,
>
> On Tue, Nov 4, 2008 at 6:09 AM, Jerome Philbert
> <jerome.philbert at gmail.com> wrote:
> > 100ms / 4.7ms = 21 messages only
> > Moreover, this is the ideal case where the CPU has nothing else to do
> than
> > sending messages ...
> > In the reality, the CPU has lots'of things to do, so I could never send
> up
> > to 21 messages.
> >
>
> On a CPU this slow, it isn't clear that libdbus is remotely usable;
> you may need a dbus implementation (or other ipc system) that is
> making different tradeoffs in the direction of efficiency. Or
> worst-case, you may need to figure out how to avoid some of the ipc.
>
> If you made a dbus library that:
> * always blocked, thus eliminating the need to build DBusMessage
> objects or maintain a message queue or deal with main loop
> * was not thread-safe, thus eliminating locking
> * was not robust against hostile peers, thus eliminating message validation
> * did not ever do checks like dbus_return_if_fail thus eliminating more
> code
> * was not safe against out-of-memory, thus eliminating even more code
> * did not try to "multiplex" code modules with "path registration" or
> "handler registration", thus killing more code and overhead
>
> I think you could have a library that was dramatically smaller and
> faster, fwiw. Basically by making it much less flexible and robust,
> and just being careful about using it. I believe an implementation of
> dbus could be pretty close to raw socket speed by making tradeoffs
> like the above.
>
> Current libdbus I'm sure can be made 30% faster or 40% faster or
> something like that, given enough effort, but if you are only getting
> 21 messages now, then even a 100% speedup would only get you to 42
> messages. If that still won't be enough, I would not dive into libdbus
> optimization, I would figure out how to somehow use dbus less.
>
> Again, we'd definitely love to see someone work on making current
> libdbus faster.
>
> Havoc
>
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