* Ingo Molnar ([email protected]) wrote:
>
> * Alan D. Brunelle <[email protected]> wrote:
>
> > o All kernels start off with Linux 2.6.23-rc6 + 2.6.23-rc6-mm1
> >
> > o '- bt cfg' or '+ bt cfg' means a kernel without or with blktrace
> > configured respectively.
> >
> > o '- markers' or '+ markers' means a kernel without or with the
> > 11-patch marker series respectively.
> >
> > 38 runs without blk traces being captured (dropped hi/lo value from 40 runs)
> >
> > Kernel Options Min val Avg val Max val Std Dev
> > ------------------ --------- --------- --------- ---------
> > - markers - bt cfg 15.349127 16.169459 16.372980 0.184417
> > + markers - bt cfg 15.280382 16.202398 16.409257 0.191861
> >
> > - markers + bt cfg 14.464366 14.754347 16.052306 0.463665
> > + markers + bt cfg 14.421765 14.644406 15.690871 0.233885
>
> actually, the pure marker overhead seems to be a regression:
>
> > - markers - bt cfg 15.349127 16.169459 16.372980 0.184417
> > + markers - bt cfg 15.280382 16.202398 16.409257 0.191861
>
> why isnt the marker near zero-cost as it should be? (as long as they are
> enabled but are not in actual use) 2% increase is _ALOT_. That's the
> whole point of good probes: they do not slow down the normal kernel.
>
> _Worst case_ it should be at most a few instructions overhead but that
> does not explain the ~2% wall-clock time regression you measured here.
>
> So there's something wrong going on - either markers have unacceptably
> high cost, or the measurement is not valid.
>
> Ingo
Hi Ingo,
Tests were executed in the following conditions:
"Taking Linux 2.6.23-rc6 + 2.6.23-rc6-mm1 as a basis, I took some sample
runs of the following on both it and after applying Mathieu Desnoyers
11-patch sequence (19 September 2007).
* 32-way IA64 + 132GiB + 10 FC adapters + 10 HP MSA 1000s (one 72GiB
volume per MSA used)"
Even though the 19 Sept. 2007 markers were released with dependency on
immediate values, there are no optimized immediate values currently
available on ia64. Therefore, we add a d-cache hit for every marker
until we merge immediate values and implement the ia64 optimization.
Mathieu
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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