[LLVMdev] On LLD performance
chisophugis at gmail.com
Mon Mar 16 23:17:45 PDT 2015
On Mon, Mar 16, 2015 at 10:52 PM, Davide Italiano <davide at freebsd.org>
> On Mon, Mar 16, 2015 at 1:54 AM, Davide Italiano <davide at freebsd.org>
> > Shankar's parallel for per-se didn't introduce any performance benefit
> > (or regression).
> > If the change I propose is safe, I would like to see Shankar's change
> > in (and this on top of it).
> > I have other related changes coming next, but I would like to tackle
> > them one at a time.
> Here's an update.
> After http://reviews.llvm.org/D8372 , I updated the profiling data.
> It seems now 85% of CPU time is spent inside
I'm rather amazed that that patch changed the total CPU time. Just doing
the work in parallel shouldn't reduce the total CPU time spent on the task.
A reduction in CPU time would happen though if parallelizing it increased
the single-threaded performance of the tasks being done in parallel.
Perhaps using multiple cores means we are using multiple caches, so each
thread is getting much better single-threaded performance due to reduced
-- Sean Silva
> In particular, 35% of the samples are spent inserting into
> unordered_map, so there's maybe something we can do differently there
> (e.g. , Rui's proposal of a concurrent map doesn't seem that bad).
> "There are no solved problems; there are only problems that are more
> or less solved" -- Henri Poincare
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
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