[petsc-dev] Cache detection

[Shri]

----- "Barry Smith" <bsmith at mcs.anl.gov> wrote:

> On Feb 3, 2010, at 4:31 AM, Jed Brown wrote:
> 
> > On Tue, 2 Feb 2010 17:28:34 -0600, Barry Smith <bsmith at mcs.anl.gov> 
> 
> > wrote:
> >>    That would be nice. :-)
> >
> > Done.  The downside of the way I'm currently doing this is that we 
> 
> > have
> > no way to tell the user that autodetection failed so we're just
> using
> > some arbitrary default.  It's not acceptable to be loud about this
> > because it doesn't make a big difference and the user is unlikely
> to
> > know these details off the top of their head (or know how to find  
> > them).
> >
> > The current defaults underestimate the values on x86-64, but my
> tests
> > (of MatMult_SeqAIJ_Inode) with incorrect line size (32 instead of
> 64)
> > show little impact.  I expect that overestimating the values (using
> 64
> > when the machine had 32) would be quite bad (maybe worse than no
> > software prefetch at all).  If issuing a bunch of prefetches is
> > expensive (e.g. I don't know what it costs on IBM hardware), then
> the
> > underestimated line sizes could hurt performance too.
> >
> > Also, I just pushed prefetch for the forward-solve part of
> > MatSolve_SeqAIJ_Inode.  For ex19, this gives me a 10-12 percent  
> > speedup
> > for the whole operation, but I was unsuccessful at speeding up the
> > back-solve using prefetch.
> >
> 
>      That's ok. There is a new MatSolve_SeqAIJ_Inode in the works that
>  
> should greatly improve the backsolve by storing the factors  
> "properly". Should be ready in a few days.
> 
  The new MatSolve_SeqAIJ_Inode is done and pushed to petsc-dev. 

>     Barry
> 
> > Jed