Re: I/O statistics per process
From: roland
Date: Thu Sep 28 2006 - 16:05:35 EST
andrew, jay - thank you very much for giving your comments on this issue and
discussing this!
I'd be interested in your opinions on all the above, please.
just kidding here a little bit (pardon!) - but from a user/admin perspective
we "just" want something like this:
http://www.my-vserver.de/stuff/linux/process-explorer.png (especially mind
the I/O columns in the middle of the screenshot)
awesome tool - but unfortunately mr. russinovich is working for the wrong
company/developing for the wrong operating system.... ;)
regards
roland
----- Original Message -----
From: "Andrew Morton" <akpm@xxxxxxxx>
To: "Jay Lan" <jlan@xxxxxxxxxxxx>
Cc: "roland" <devzero@xxxxxx>; "Fengguang Wu" <fengguang.wu@xxxxxxxxx>;
<linux-kernel@xxxxxxxxxxxxxxx>; <lserinol@xxxxxxxxx>
Sent: Thursday, September 28, 2006 9:09 PM
Subject: Re: I/O statistics per process
On Thu, 28 Sep 2006 11:55:38 -0700
Jay Lan <jlan@xxxxxxxxxxxx> wrote:
Andrew Morton wrote:
> On Wed, 27 Sep 2006 23:22:02 +0200
> "roland" <devzero@xxxxxx> wrote:
>
>>thanks. tried to contact redflag, but they don`t answer. maybe support
>>is
>>being on holiday.... !?
>>
>>linux kernel hackers - there is really no standard way to watch i/o
>>metrics
>>(bytes read/written) at process level?
>
> The patch csa-accounting-taskstats-update.patch in current -mm kernels
> (whcih is planned for 2.6.19) does have per-process chars-read and
> chars-written accounting ("Extended accounting fields"). That's
> probably
> not waht you really want, although it might tell you what you want to
> know.
>
>>it`s extremly hard for the admin to track down, what process is hogging
>>the
>>disk - especially if there is more than one task consuming cpu.
Rolend,
The per-process chars-read and chars-writeen accounting is made
available through taskstats interface (see Documentation/accounting/
taskstats.txt) in 2.6.18-mm1 kernel. Unfortunately, the user-space CSA
package is still a few months away. You may, for now, write your
own taskstats application or go a long way to port the in-kernel
implementation of pagg/job/csa.
However, the "Externded acocunting fields" patch does not provide you
straight forward answer. The patch provides accounting data only at
process termination (just like the BSD accounting) and it seems that
you want to see which run-away application (ie, alive) eating up your
disk. The taskstats interface offers a query mode (command-response),
but currently only delayacct uses that mode. We would need to make
those data available in the query mode in order for application to
see accounting data of live processes.
ow. That is a rather important enhancement to have.
>
> csa-accounting-taskstats-update.patch makes that information available
> to
> userspace.
>
> But it's approximate, because
>
> - it doesn't account for disk readahead
>
> - it doesn't account for pagefault-initiated reads (althought it easily
> could - Jay?)
>
> - it overaccounts for a process writing to an already-dirty page.
>
> (We could fix this too: nuke the existing stuff and do
>
> current->wchar += PAGE_CACHE_SIZE;
>
> in __set_page_dirty_[no]buffers().) (But that ends up being wrong if
> someone truncates the file before it got written)
>
> - it doesn't account for file readahead (although it easily could)
>
> - it doesn't account for pagefault-initiated readahead (it could)
>
>
> hm. There's actually quite a lot we could do here to make these fields
> more accurate and useful. A lot of this depends on what the definition
> of
> these fields _is_. Is is just for disk IO? Is it supposed to include
> console IO, or what?
I'd be interested in your opinions on all the above, please.
-
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