Re: 2.5.34-mm4

[Andrew Morton]

Rik van Riel wrote:
> 
> On Sun, 15 Sep 2002, M. Edward Borasky wrote:
> 
> > Borasky's Corollary 1: If you *can* measure it and it *does* exist, the
> > cheapest solution may still be to buy more memory, more disks or a
> > faster processor.
> 
> Current 2.5 is sluggish on systems with a fast CPU and 768 MB
> of RAM, whereas current -ac runs the same workload smoothly
> with 128 MB of RAM.
> 

I've been running 2.5 on my desktop at work (800MHz/256M UP) since
2.5.26 and on the machine at home (Dual 850MHz/768M) on-and-off
(recent freizures sent that machine back to Marcelo; need to try
again).  I also ran 2.4.19-ac-something for a couple of weeks.

Impressions are:

- 2.5 swaps a lot in response to heavy pagecache activity.

  SEGQ didn't change that, actually.  And this is correct,
  as-designed behaviour.  We'll need some "don't be irritating"
  knob to prevent this.  Or speculative pagein when the load
  has subsided, which would be a fair-sized project.

- In both -ac and 2.5 the scheduler is prone to starving interactive
  applications (netscape 4, gkrellm, command-line gdb, others) when
  there is a compilation happening.

  This is very, very noticeable; and it afects applications which
  do not use sched_yield().  Ingo has put some extra stuff in since
  then and I need to retest.

- In -ac, there are noticeable stalls during heavy writeout.  This
  may be an ext3 thing, but I can't think of any IO scheduling
  differences in -ac ext3.  I'd be guessing that it is due to
  bdflush/kupdate lumpiness.

Overall I find Marcelo kernels to be the most comfortable, followed
by 2.5.  Alan's kernels I find to be the least comfortable in a
"developer's desktop" situation.