[test-suite] r241675 - [LNT] Reduce I/O execution time for Polybench

[Kristof Beyls]

It also has the nice side-effect that it makes the performance
tracking bots produce numbers about 5% faster. :)

> -----Original Message-----
> From: llvm-commits-bounces at cs.uiuc.edu [mailto:llvm-commits-
> bounces at cs.uiuc.edu] On Behalf Of Tobias Grosser
> Sent: 09 July 2015 00:10
> To: llvm-commits at cs.uiuc.edu; polly-dev
> Subject: Re: [test-suite] r241675 - [LNT] Reduce I/O execution time for
> Polybench
> 
> On 07/08/2015 12:21 PM, Renato Golin wrote:
> > Author: rengolin
> > Date: Wed Jul  8 05:21:42 2015
> > New Revision: 241675
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=241675&view=rev
> > Log:
> > [LNT] Reduce I/O execution time for Polybench
> >
> > Polybench had large execution time due to the successive call to
> > fprintf as much as 4000*4000 times. For most programs, this was more
> > than 1/2 of its execution time.
> >
> > The current solution is to transform the values into a stream of
> > nibbles as a char string, and print it once for every row, ie.
> > only as much as 4000 times, by using fputs instead of fprintf.
> >
> > Overall new execution time is 47% of previous with some as low as 5%.
> > The reduction on x86_64 was 53%, on ARM was 51% and on AArch64 was
> > 55%, which means most of the time was spent on I/O, not the actual
> benchmark.
> >
> > Test fdtd-apml was not converted because it's not bit identical across
> > platforms, but it should be. Adding a FIXME. Other tests were not
> > converted due to regressing in run time for being too simple/small
> > even on our slowest targets.
> 
> Very nice. This change makes Polly really shine on polybench:
> 
> http://llvm.org/perf/db_default/v4/nts/29988?compare_to=29985
> 
> Best,
> Tobias
> 
> 
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