[Bug tree-optimization/19794] [meta-bug] Jump threading related bugs

["law at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From law at redhat dot com  2005-04-06 00:25 -------
Just more notes on the huge perl speedup with the threading changes...

For reasons yet unknown, we're seeing a lot less L2 cache traffic when perl
is compiled with the threading changes.  The decreased L2 traffic also
corresponds to the areas of code which I had previously identified as
showing the most significant runtime improvements.

What I don't have an answer for yet is _why_ we're seeing the huge decrease
in L2 traffic.  We're seeing a huge jump in MEMORY_CANCEL events, which if
I understand the docs correctly will cause an increase in cache activity as
we are either low on store buffers or we have conflicts due to 64k aliasing.
[Both sub-events are way-down with the threading changes. ]

Attempts to perturb the size of the stack for the recursive routine in question
to avoid the 64k aliasing problem haven't met with any success yet.  We are
seeing variables spilled into different stack locations, so that _could_ be
the ultimate cause of the cache behavior.  These things would definitely
classify as secondary order effects

We're also seeing a measurable decrease in ITLB misses, howerver, I'm not
convinced that the decrease is significant enough to cause the kind of
performance improvement we're seeing.

Anyway, I'm still plugging away...

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19794