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SubjectRe: Finding what is stuck...
On Mon, 1 Sep 2008 17:08:12 -0700, Arjan van de Ven <arjan@infradead.org> wrote:

> On Tue, 2 Sep 2008 02:04:47 +0200
> "J.A. Magallón" <jamagallon@ono.com> wrote:
>
> > Hi all...
> >
> > I'm running 2.6.27-rc5-git2 on an Aspire One.
> > The system is in general pretty responsive, but sometimes it just gets
> > totally stuck. Even the mouse stops.
> >
> > It looks related to disk (SSD) access, but I'm not totally sure.
> > Is there any way to find what is getting stuck ? I know that SSDs can
> > be slow on write, I don't mind if the system is faster or slower
> > (it's small :))), but if the speed is constant. That occasional
> > pauses are strange, like if SSD flushing gets stuck on BKL
> > (I know, no idea about what I talk...).
> >
> > I'm using ext3 fs, noop iosched. But as I say, I'm not sure that the
> > disk writes are the culprit.
> >
> > Any idea about how to find this ?
>
> Have you tried to run "latencytop"?
> (you need to enable this in the kernel config as well)
>
> it tends to (for me at least) point out very well where stalls happen,
> or at least, what the system is doing when they happen.
>
> (hint: make sure you do "make install" before running it)
>

These are some shots of latencytop while working. I copied the screen
when I saw any very high timing...

Cause Maximum Percentage
Walking directory tree 790.2 msec 10.6 %
Scheduler: waiting for cpu 40.5 msec 38.5 %

fsync() on a file 3191.6 msec 36.7 %
Reading EXT3 directory 1553.3 msec 3.9 %
EXT3: Waiting for journal access 1518.7 msec 3.8 %
Deleting an inode 657.5 msec 1.7 %
EXT3: Looking for file 576.3 msec 1.4 %
Writing a page to disk 363.0 msec 6.1 %
call_usermodehelper_exec request_module __sock_cre 69.4 msec 0.2 %
Scheduler: waiting for cpull 28.0 msec 18.9 %
Page fault 7.9 msec 0.3 %

fsync() on a file 8843.7 msec 81.8 %
Writing a page to disk 1548.6 msec 2.9 %
EXT3: Waiting for journal access 356.5 msec 1.1 %
Scheduler: waiting for cpu 40.6 msec 6.0 %

EXT3: Waiting for journal access 6153.6 msec 17.2 %
fsync() on a file 4902.7 msec 53.5 %
Writing a page to disk 3487.2 msec 9.8 %
Writing buffer to disk (synchronous) 2288.7 msec 4.6 %
synchronous write 1320.6 msec 2.6 %
Truncating file 302.6 msec 0.6 %
Page fault 290.5 msec 0.6 %
Scheduler: waiting for cpu 13.4 msec 4.5 %
Waiting for event (select) 5.0 msec 5.0 %

Deleting an inode 5584.7 msec 27.5 %
Writing a page to disk 829.2 msec 5.4 %
fsync() on a file 265.1 msec 11.2 %
Scheduler: waiting for cpu 37.2 msec 11.5 %
stat() operation 5.6 msec 0.1 %
Page fault 5.5 msec 0.2 %
Waiting for event (select) 5.0 msec 39.8 %
Waiting for event (poll) 5.0 msec 2.5 %
synchronous write 4.2 msec 0.0 %

All look fs access:

one:~# df
Filesystem Type Size Used Avail Use% Mounted on
/dev/sda1 ext3 6.9G 3.7G 3.2G 55% /
tmpfs tmpfs 246M 12K 246M 1% /tmp
/dev/mmcblk0p1
ext3 1.9G 35M 1.8G 2% /store

I will try mounting root as ext2, to rule out jorunaling...

TIA

--
J.A. Magallon \ Software is like sex:
\ It's better when it's free
Mandriva Linux release 2008.1 (Cooker) for i586
Linux kernel 2.6.23-jam01, gcc version 4.2.2 20070909
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