Re: [Bug #11308] tbench regression on each kernel release from 2.6.22 -> 2.6.28

David Miller
2008-11-17T09:14:03Z

From: Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>
Date: Mon, 17 Nov 2008 10:06:48 +0100

>
> * Rafael J. Wysocki <rjw-KKrjLPT3xs0@public.gmane.org> wrote:
>
> > This message has been generated automatically as a part of a report
> > of regressions introduced between 2.6.26 and 2.6.27.
> >
> > The following bug entry is on the current list of known regressions
> > introduced between 2.6.26 and 2.6.27. Please verify if it still should
> > be listed and let me know (either way).
> >
> >
> > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=11308
> > Subject : tbench regression on each kernel release from 2.6.22 -&gt; 2.6.28
> > Submitter : Christoph Lameter <cl-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
> > Date : 2008-08-11 18:36 (98 days old)
> > References : http://marc.info/?l=linux-kernel&m=121847986119495&w=4
> > http://marc.info/?l=linux-kernel&m=122125737421332&w=4
>
> Christoph, as per the recent analysis of Mike:
>
> http://fixunix.com/kernel/556867-regression-benchmark-throughput-loss-a622cf6-f7160c7-pull.html
>
> all scheduler components of this regression have been eliminated.
>
> In fact his numbers show that scheduler speedups since 2.6.22 have
> offset and hidden most other sources of tbench regression. (i.e. the
> scheduler portion got 5% faster, hence it was able to offset a
> slowdown of 5% in other areas of the kernel that tbench triggers)

Although I respect the improvements, wake_up() is still several orders
of magnitude slower than it was in 2.6.22 and wake_up() is at the top
of the profiles in tbench runs.

It really is premature to close this regression at this time.

I am working with every spare moment I have to try and nail this
stuff, but unless someone else helps me people need to be patient.