[systemd-devel] sd-bus vs gdbus on dbus-daemon

[Umut Tezduyar Lindskog]

Hi Simon,

On Wed, Apr 29, 2015 at 5:34 PM, Simon McVittie
<simon.mcvittie at collabora.co.uk> wrote:
> On 29/04/15 15:08, Umut Tezduyar Lindskog wrote:
>> We [1] have noticed that there could be up to %50 performance gain on
>> using sd-bus over gdbus on dbus-daemon.
> ...
>> gdbus.c
>>   - g_dbus_proxy_new_for_bus_sync()
>>   - 50 x g_dbus_proxy_call_sync()
>>
>> sdbus.c
>>   - sd_bus_open_system()
>>   - 50 x sd_bus_get_property()
>
> If you want to "compare apples with apples", I suggest using the
> lower-level g_bus_get() and g_dbus_connection_call[_sync]() instead of
> GDBusProxy. The design and priorities of sd-bus and GDBus are not really
> very similar, but GDBusProxy is certainly not the closest equivalent you
> can get.

Thanks for the tip. I will re-run the measurements with
g_dbus_connection_call_sync(g_bus_get_sync(),...). Just considering
the traffic in the dbus, I do believe we have compared apple to apple.
But if you believe we might get even more performance with raw API
calls, then that is fantastic news!

>
> Also, if your application profile is such that (a) D-Bus is a
> significant factor in performance, and (b) sending 50 synchronous D-Bus
> messages per connection is anywhere near realistic, then you are
> probably not using D-Bus the way it is designed to be used.

Measurement we have done was not about if dbus is the ipc we want or
not. It was about comparing the performances of two libraries. It
wouldn't have been fair to compare sending only 1 message on the dbus
due to the performance penalty of creating a worker thread with gdbus.
But it really didn't matter. 1, 2, 10, 50, in all cases gdbus
(GDBusProxy) couldn't performed as good as sd-bus.

>
> See also <http://permalink.gmane.org/gmane.comp.freedesktop.dbus/13663>.
>
> --
> Simon McVittie
> Collabora Ltd. <http://www.collabora.com/>
>
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