This is the mail archive of the mailing list for the GCC project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Patch to Avoid Bad Prefetching


> > I think it would be better to use expected_loop_iterations if the
> > estimate is not available, rather than introducing a new param
> > (while it is likely not more precise, we have way too many params
> > as it is).
> > I agree.  IMHO for prefetching we should recommend profile-feedback.
> The point is that in the prefetching profitability analysis, we must
> have a very conservative estimate for unknown trip counts or we may
> get a big performance degradation as shown in the benchmark numbers I
> included. By conservative, I mean something like 3 or 4 iterations
> only.  In other words, if we don't know the trip count, we should
> assume the worse in this particular analysis to avoid seriously
> degradaing performance. I wonder how the estimate of
> expected_loop_iterations is computed and whether it gives us the
> conservative estimate that we need here?

in the absence of any other hints obtained from the program, the
loops are predicted to iterate 10 times,


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]