linux-kernel - Re: Finding what is stuck...

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Date:	Wed, 3 Sep 2008 16:50:14 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	"J.A. Magallón" <jamagallon@....com>
Cc:	Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Finding what is stuck...

On Thu, 4 Sep 2008 01:00:43 +0200
"J.A. Magallón" <jamagallon@....com> wrote:

> On Mon, 1 Sep 2008 17:08:12 -0700, Arjan van de Ven
> <arjan@...radead.org> wrote:
> 
> > On Tue, 2 Sep 2008 02:04:47 +0200
> > "J.A. Magallón" <jamagallon@....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...
> 

wow bad ones..

one thing to note.. you have *something* doing fsync() a lot it seems
(latencytop is likely to tell you which one it is); fsync on ext3 is
really expensive, especially on an ssd that is slow to write to.


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