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SubjectRe: anticipatory scheduling questions
----- Original Message ----- 
From: Andrew Morton <akpm@digeo.com>
Date: Sat, 1 Mar 2003 02:40:24 -0800
To: "Felipe Alfaro Solana" <felipe_alfaro@linuxmail.org>
Subject: Re: anticipatory scheduling questions

> "Felipe Alfaro Solana" <felipe_alfaro@linuxmail.org> wrote:
> >
> > ----- Original Message -----
> > > Does basic 2.5.63 do the same thing? Do you have a feel
> > > for when it started happening?
> >
> > This has happened since the moment I switched from
> > 2.4 to 2.5.63-mm1.
>
> You have not actually said whether 2.5.63 base exhibits
> the same problem. From the vmstat traces it appears
> that the answer is "yes"?

Both 2.5.63 and 2.5.63-mm1 exhibit this behavior, but
can't be reproduced with 2.4.20-2.54.

> > I have retested this with 2.4.20-2.54, 2.5.63 and 2.5.63-mm1...
> > and have attached the files to this message
>
> Thanks. Note how 2.4 is consuming a few percent CPU, whereas 2.5 is
> consuming 100%. Approximately half of it system time.

It seems is not "user" or "system" time what's being consumed, it's
"iowait" Look below :-)

> It does appear that some change in 2.5 has caused evolution to go berserk
> during this operation.

I wouldn't say it's exactly Evolution what's going berserk. Doing a
"top -s1" while trying to reply to a big e-mail message, I've noticed
that "top" reports "iowait" starting at ~50%, then going up very fast
and then staying up at 90-95% all the time. This happens on 2.5.63
and 2.5.63-mm1, however, on 2.4.20-2.54 kernel, "iowait" stays all
the time exactly at "0%" and idle time remains steady at 90-95%.

These measures were taken using "top" with a delay of 1 second,
starting at the moment in which I try replying to a large e-mail
message.

> The next step please is:
>
> a) run top during the operation, work out which process is chewing all
> that CPU. Presumably it will be evolution or aspell

Well, the "top" command reveals that Evolution is taking very
little CPU usage (between 1 and 6%). Nearly all the time is
accounted under "iowait".

The other Evolution processes top at a peak sum of 5% of
CPU usage, more or less.

> b) Do it again and this time run
> strace -p $(pidof evolution) # or aspell

I think this is going to be difficult... as I said Evolution is a very
complex program and it spawns a lot of processes. When I
click the Reply, Evolution spawns two processes:
"gnome-gtkhtml-editor" and "gnome-spell-component".

I have little experience with process tracing and don't know
how to attach to those processes from the very beginning.
Attaching to the main Evolution process doesn't help: the "strace"
command dumps a lot of info when Evolution starts up, but
starts being useless at the moment I click the Reply and Evolution
spawns these two new processes to process the request.

Any ideas?

> This will tell us what it is up to.

I'm sorry I can't help much more. Can you give me more
pointers on how to nail this down?

Thanks!

Felipe Alfaro Solana

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