Missing the AF_BUS [LWN.net]

Missing the AF_BUS

Posted Jul 26, 2012 22:41 UTC (Thu) by oak (subscriber, #2786)
In reply to: Missing the AF_BUS by hp
Parent article: Missing the AF_BUS

> When I've asked for concrete examples of when it was a problem, things like Nokia N900 (iPhone 3G era hardware right?) come up

One of the worst issues is D-BUS message delivery reliability. All it needs is an app that subscribes for some frequent message (like device orientation) and then doesn't read its messages either because it was supended or just buggy. As message delivery needs to be reliable, D-BUS will then just buffer the messages and get all the time slower and slower as it starts to swap.

Second issue is too complicated D-BUS setup. I think e.g. the N900 call handling goes through half a dozen daemons before the call UI pops up. Each of these steps adds it's own socket buffering and process scheduling overhead in addition to other overheads (e.g. paging the processes in to RAM if they were swapped out etc).

Then there's the D-BUS daemon code itself. Ever wondered why something that's "just" supposed to read and write data from sockets is CPU bound instead of IO bound? D-BUS daemon spends a lot of CPU on message content marshaling.

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Missing the AF_BUS

Posted Jul 26, 2012 22:57 UTC (Thu) by hp (subscriber, #5220) [Link]

the tradeoffs in the first issue can be configured in the config
file, it can throw errors when the buffer size is whatever you like. there are also some list/bug discussions of other behaviors that could be useful to support.

the second issue is not dbus's fault. that kind of thing is often from making a daemon when a library would be better. it's a bug in the app design.

the third issue I've mentioned repeatedly myself including in the threads I linked before.

but none of these three thing are concrete examples of user visible operations. in most real world cases all three of these problems are gotten away with and it isn't perceptible. n900 is the most often mentioned case where they aren't and if you're correct here, N900 has at least one really bad setup with half a dozen daemons.