924091 - Heavy CPU load during download

Status: NEW

(Toolkit :: Downloads API, defect)

Description

[Honza Bambas (:mayhemer)]

Attachment: download-cpu-load.zip

I was downloading http://adcdownload.apple.com/Developer_Tools/command_line_tools_os_x_lion_for_xcode__april_2013/xcode462_cltools_10_76938260a.dmg on my mac (10.7.5, to this date nightly, http://hg.mozilla.org/mozilla-central/rev/5f0569c3cb8f, new cache enabled).

There was a significant (but not 100%) load of the CPU.  UI was janking.

I'm attaching a profile captured by web tools profiler.

Comment 1

[:Paolo Amadini]

I think that bug 917012 might help a little bit, in that it avoids duplicate computations, even though it seems from the profile that you hadn't the Library window open while downloading, so the gain will be minor.

We are planning to simplify the user interface code, this might also help. If the load is still significant with bug 917012 applied, feel free to attach a new profile and leave this bug open while we figure out if we can improve something there. Progress updates are already throttled, I'm not sure there is much more we can do.

You may also try to put an early "return" in the "_setBytes" function of "DownloadCore.jsm" and see if the overall CPU load is due to progress updates or there is something else that contributes the CPU load in the process, maybe background file I/O.