Re: page table lock patch V15 [0/7]: overview

[Christoph Lameter]

On Wed, 12 Jan 2005, Christoph Hellwig wrote:

> On Wed, Jan 12, 2005 at 08:39:21AM -0800, Christoph Lameter wrote:
> > The future is in higher and higher SMP counts since the chase for the
> > higher clock frequency has ended. We will increasingly see multi-core
> > cpus etc. Machines with higher CPU counts are becoming common in business.
>
> An they still are absolutely in the minority.  In fact with multicore
> cpus it becomes more and more important to be fast for SMP systtems with
> a _small_ number of CPUs, while really larget CPUs will remain a small
> nische for the forseeable future.

The benefits start to be significant pretty fast with even a few cpus
on modern architectures:

Altix  no patch:
 Gb Rep Threads   User      System     Wall flt/cpu/s fault/wsec
  1  10    1    0.107s      6.444s   6.055s100028.084 100006.622
  1  10    2    0.121s      9.048s   4.082s 71468.414 135904.412
  1  10    4    0.129s     10.185s   3.011s 63531.985 210146.600

w/patch
 Gb Rep Threads   User      System     Wall flt/cpu/s fault/wsec
  1  10    1    0.094s      6.116s   6.021s105517.039 105517.574
  1  10    2    0.134s      6.998s   3.087s 91879.573 169079.712
  1  10    4    0.095s      7.658s   2.043s 84519.939 268955.165

There is even a small benefit to the single thread case.

Its not the case that this patch only benefits systems with a large number
of CPUs. Of course that is when the benefits results in performance gains
by orders of magnitude.

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