[petsc-dev] Fwd: [Xlab] slow pagefault on KNC

[Jed Brown]

He should be using all the threads for this. Using one thread to fault a
bunch of memory is a recipe for terrible performance all around.


On Mon, Dec 17, 2012 at 9:21 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>    Should we have a test like this in the PETSc benchmark directory?
>
>    Barry
>
>
> Begin forwarded message:
>
> > From: Kazutomo Yoshii <kazutomo at mcs.anl.gov>
> > Subject: [Xlab] slow pagefault on KNC
> > Date: December 17, 2012 10:48:06 AM CST
> > To: "xlab at cels.anl.gov" <xlab at cels.anl.gov>
> >
> > Hi,
> >
> > I noticed that pagefault is very slow on KNC.  It takes 850 usec
> > while it takes ~1 usec on Xeon, so prefaulting 1GB of memory region
> > takes 222 sec on KNC.
> >
> > This may not impact a big app runs for hours and hours, but I guess
> > this definitely affects short-lived processes or threads, which might
> > make MIC less fascinating.
> >
> > This could be a hardware problem(need to check Phi), a kernel bug,
> > or maybe sage of SMP kernel on many-core.
> > If this is the last case, it would be really interesting for me.
> >
> > Attached a simple page fault benchmark.
> >
> > - kaz
> [see attached file:
> pftest.c]_______________________________________________
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> > https://lists.cels.anl.gov/mailman/listinfo/xlab
>
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