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List:       kdepim-users
Subject:    Re: [kdepim-users] KMail + IMAP painfully slow [trace info]
From:       Ingo =?iso-8859-1?q?Kl=F6cker?= <kloecker () kde ! org>
Date:       2007-05-21 20:21:01
Message-ID: 200705212221.03130 () erwin ! ingo-kloecker ! de
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On Thursday 17 May 2007 07:40, Ross Boylan wrote:
> I downloaded some debug symbols and attached to kmail at various
> times.  Here are the results.  I don't know if this is enough info to
> be helpful.
[snip]
> 2) Entered a search string in the quick search box.  It was
> particularly suprising this stalled, since it was my main INBOX, I
> thought no other operations were happening (e.g., action described in
> 1 above seemed to have finished), and the box was already encountered
> and indexed.  I've put some comments with ##
> (gdb) attach 12886
> Attaching to program: /usr/bin/kmail, process 12886
> [New Thread -1248798496 (LWP 12886)]
> [New Thread -1288971344 (LWP 12890)]
> [New Thread -1280578640 (LWP 12889)]
> [New Thread -1272185936 (LWP 12888)]
> [New Thread -1263793232 (LWP 12887)]
> Loaded symbols for /usr/lib/libkmailprivate.so
> ## I had previously attached and detached for the report of item 1).
> ## This looks as if more than one thread was going.
> ## Many symbol loading messages omitted.
> Loaded symbols for /usr/lib/libgcrypt.so.11
> Failed to read a valid object file image from memory.
> [Switching to Thread -1248798496 (LWP 12886)]
> 0xb721c714 in QListViewItem::itemAbove (this=0xa8034e8) at
> widgets/qlistview.cpp:3922
> 3922    widgets/qlistview.cpp: No such file or directory.
>         in widgets/qlistview.cpp
> (gdb) where
> ## note the next few # lines are from gdb, not me
> #0  0xb721c714 in QListViewItem::itemAbove (this=0xa8034e8) at
> widgets/qlistview.cpp:3922
> #1  0xb721c7b9 in QListViewItem::itemAbove (this=0xab3bf00) at
> widgets/qlistview.cpp:3933
> #2  0xb721c7b9 in QListViewItem::itemAbove (this=0xab3beb8) at
> widgets/qlistview.cpp:3933
> #3  0xb721c7b9 in QListViewItem::itemAbove (this=0xa2c9170) at
> widgets/qlistview.cpp:3933
> ## These just kept going; I stopped the output at 496.
> ## This looks as if itemAbove has gone crazy with recursion.
> ## I guess if it is following the list of items up this is possible,
> ## though it certainly seems undesirable.  If there is a
> QListViewItem for ## every message in the message, that certainly
> could explain some of the ## problems I've been having.  There were
> way more than 496 messages in the ## box, though way less than that
> many items visible.

QListViewItem::itemAbove() is known to be slow. 
(http://doc.trolltech.com/3.3/qlistviewitem.html#itemAbove)

> A proper solution to this would probably use a kind of database
> display logic, since that is another situation where you have tons of
> records and only want to display a few of them at a time.  Actually
> creating and painting the interface elements for every item in the
> box (since one might scroll there) is clearly prohibitive.

This will all change with KDE 4. The Model/View approach introduced with 
Qt 4 will make this much more sane and fast.

> 3) I discovered that if you click the progress bar on the bottom
> right you get detailed reports of what's going on and what's waiting.
>  When I moved a message to a new folder, this progress bar confirmed
> that kmail was busy getting information for that folder (which took
> forever).

Yeah, opening a target folder could probably be optimized.

> 4) This isn't exactly a user question, but I'm curious why kmail uses
> the Qt mechanism Ingo described rather than real threads.   Is that
> just to save the hassle of ensuring that all threads do UI updates
> only via the main thread?

I can't give you a definitive answer. It's probably a combination of 
historical reasons (threads were not really usable when KMail was 
started more than 10 years ago) and the fact that the Qt mechanism is 
really easy to use.

Regards,
Ingo

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