2.4.4+fork patch still sluggish

2.4.4+fork patch still sluggish

[Jeffrey Kuskin]

This is basically a followup to the "2.4.4 sluggish under fork load"
thread.

I am using Redhat 7.1 on a 128MB 400 MHz PII system.  I have a
locally-built 2.4.4 kernel to which I manually applied the patch that backs
out the child-before-parent behavior on a fork.  Namely, this patch:

  <http://boudicca.tux.org/hypermail/linux-kernel/2001week17/1288.html>

However, even with this patch applied, I still see extremley jerky mouse
pointer behavior when I run any kind of job that does lots of forking.  For
example, a kernel compile or even just the "configure" in preparation for
compiling XEmacs.

The same behavior, on exactly the same machine, did _not_ occur with Redhat
6.2/kernel 2.2.19.

I see that this patch has recently been merged into 2.4.5-pre1, but I am
concerned that it does actually fix the underlying problem.

Do others continue to see "jerky mouse pointer" behavior even with this
patch installed, or should I look for other causes?  For instance, are
there known problems with jerky mouse pointer behavior under heavy swapping
load?

-- 
Jeffrey Kuskin                              Tel: +1-408-773-5256
Senior System Engineer                      Fax: +1-408-773-9940
Atheros Communications                      http://www.atheros.com
jsk@atheros.com

Re: 2.4.4+fork patch still sluggish

[Andrea Arcangeli]

On Thu, May 03, 2001 at 06:38:27PM -0700, Jeffrey Kuskin wrote:
> This is basically a followup to the "2.4.4 sluggish under fork load"
> thread.
> 
> I am using Redhat 7.1 on a 128MB 400 MHz PII system.  I have a
> locally-built 2.4.4 kernel to which I manually applied the patch that backs
> out the child-before-parent behavior on a fork.  Namely, this patch:
> 
>   <http://boudicca.tux.org/hypermail/linux-kernel/2001week17/1288.html>
> 
> However, even with this patch applied, I still see extremley jerky mouse
> pointer behavior when I run any kind of job that does lots of forking.  For
> example, a kernel compile or even just the "configure" in preparation for
> compiling XEmacs.
> 
> The same behavior, on exactly the same machine, did _not_ occur with Redhat
> 6.2/kernel 2.2.19.
> 
> I see that this patch has recently been merged into 2.4.5-pre1, but I am
> concerned that it does actually fix the underlying problem.
> 
> Do others continue to see "jerky mouse pointer" behavior even with this
> patch installed, or should I look for other causes?  For instance, are
> there known problems with jerky mouse pointer behavior under heavy swapping
> load?

That's a bug in the get-child-timeslice logic that I mentioned a few
days ago.

Interesting strict fixes for this issue are here (they won't apply
cleanly to 2.4.5pre1 but fixing reject is trivial):

	ftp://ftp.us.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.4/2.4.5pre1aa1/10_parent-timeslice-6
	ftp://ftp.us.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.4/2.4.5pre1aa1/20_share-timeslice-2

If you can reproduce on 2.4.5pre1aa1 let us know. Thanks!

Andrea