Canonical System Image

Bug #1480844
Comment #4

Comment 4 for bug 1480844

Revision history for this message

Michael Terry (mterry) wrote on 2015-08-24:

This has been bugging me. Here are some facts, followed by speculation:

= Facts =

- I have a mako, using latest stable channel image (at time of this writing, 22 -- OTA5 in other words).

- A reboot will fix it for some amount of time.

- I can reproduce this fairly reliably. Especially when walking around my neighborhood (a busy urban area). For example, I watched it start happening this morning when leaving the subway and entering my neighborhood.

- I've attached a screenshot of 'top' when this happened to me once. It shows dbus-daemon at 100% cpu. Other processes occasionally flair up briefly, but settle down shortly. dbus-daemon is constant though.

- I've looked at top other instances of this bug, and it looks the same. So I think it's reliably dbus-daemon that is the 100% cpu culprit.

- It really takes a toll on wifi detection. I walked from my apartment to a coffee shop. And hit this bug on the way. Once in the coffee shop, I wanted to make sure I was using the shop's wifi. I opened the network indicator, and boy was it having a hard time. It was showing me still connected to my home network. And slowly started updating with wifi networks along the way to the shop. In chunks of updates, not smoothly. It *eventually* got to the shop's wifi, but only after at least a minute I recall. A real minute, not a fake 10s, it-felt-like-forever minute.

= Speculation =

- I think this is switching-network related (or maybe just a bunch of wifi networks coming in and out of scan range?). When I left the subway into my neighborhood, I went from 3G->wifi (for a nearby shop I've connected to before). When I walk in my neighborhood, I'm both connecting to temporary wifi (for shops I pass that I've been to before), and just scanning a bunch of networks (for shops that I've not connected to before, but line the street).

- This may be confirmation bias, or just the daemon trying to keep up, but it feels like NetworkManager spikes CPU in 'top' more than other processes like unity8. Nothing comes close to dbus-daemon, but still.

This has been bugging me.  Here are some facts, followed by speculation:

= Facts =

- I have a mako, using latest stable channel image (at time of this writing, 22 -- OTA5 in other words).

- A reboot will fix it for some amount of time.

- I can reproduce this fairly reliably.  Especially when walking around my neighborhood (a busy urban area).  For example, I watched it start happening this morning when leaving the subway and entering my neighborhood.

- I've attached a screenshot of 'top' when this happened to me once.  It shows dbus-daemon at 100% cpu.  Other processes occasionally flair up briefly, but settle down shortly.  dbus-daemon is constant though.

- I've looked at top other instances of this bug, and it looks the same.  So I think it's reliably dbus-daemon that is the 100% cpu culprit.

- It really takes a toll on wifi detection.  I walked from my apartment to a coffee shop.  And hit this bug on the way.  Once in the coffee shop, I wanted to make sure I was using the shop's wifi.  I opened the network indicator, and boy was it having a hard time.  It was showing me still connected to my home network.  And slowly started updating with wifi networks along the way to the shop.  In chunks of updates, not smoothly.  It *eventually* got to the shop's wifi, but only after at least a minute I recall.  A real minute, not a fake 10s, it-felt-like-forever minute.

= Speculation =

- I think this is switching-network related (or maybe just a bunch of wifi networks coming in and out of scan range?).  When I left the subway into my neighborhood, I went from 3G->wifi (for a nearby shop I've connected to before).  When I walk in my neighborhood, I'm both connecting to temporary wifi (for shops I pass that I've been to before), and just scanning a bunch of networks (for shops that I've not connected to before, but line the street).