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Hi Keno,<br>
<br>
Thanks for the fast ISel suggestion.<br>
<br>
Here are the results (for a small but representational run):<br>
<br>
LLVM 3.5.2 (old JIT): 4m44s<br>
<br>
LLVM 3.7.1 (MCJit) no fast ISel: 7m31s<br>
<br>
LLVM 3.7.1 (MCJit) fast ISel: 7m39s<br>
<br>
So not much of a difference unfortunately.<br>
<br>
<div class="moz-cite-prefix">On 05/02/16 11:05, Keno Fischer wrote:<br>
</div>
<blockquote
cite="mid:CAEoGj__gD=t2Ay5LKjcH9_7tp4p_AHUoxTgpYBRrHCc8479Nwg@mail.gmail.com"
type="cite">
<div dir="ltr">Yes, unfortunately, this is very much known. Over
in the julia project, we've recently gone through this and taken
the hit (after doing some work to fix the very extreme corner
cases that we were hitting). We're not entirely sure why the
slowdown is this noticable, but at least in our case, profiling
didn't reveal any remaining low hanging fruits that are
responsible. One thing you can potentially try if you haven't
yet is to enable fast ISel and see if that brings you closer to
the old runtimes.</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Thu, Feb 4, 2016 at 7:00 PM, Morten
Brodersen via llvm-dev <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:llvm-dev@lists.llvm.org" target="_blank"><a class="moz-txt-link-abbreviated" href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a></a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Hi All,<br>
<br>
We recently upgraded a number of applications from LLVM
3.5.2 (old JIT) to LLVM 3.7.1 (MCJit).<br>
<br>
We made the minimum changes needed for the switch (no
changes to the IR generated or the IR optimizations
applied).<br>
<br>
The resulting code pass all tests (8000+).<br>
<br>
However the runtime performance dropped significantly: 30%
to 40% for all applications.<br>
<br>
The applications I am talking about optimize airline rosters
and pairings. LLVM is used for compiling high level business
rules to efficient machine code.<br>
<br>
A typical optimization run takes 6 to 8 hours. So a 30% to
40% reduction in speed has real impact (=> we can't
upgrade from 3.5.2).<br>
<br>
We have triple checked and reviewed the changes we made from
old JIT to MCJIt. We also tried different ways to optimize
the IR.<br>
<br>
However all results indicate that the performance drop
happens in the (black box) IR to machine code stage.<br>
<br>
So my question is if the runtime performance reduction is
known/expected for MCJit vs. old JIT? Or if we might be
doing something wrong?<br>
<br>
If you need more information, in order to understand the
issue, please tell us so that we can provide you with more
details.<br>
<br>
Thanks<br>
Morten<br>
<br>
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</blockquote>
</div>
<br>
</div>
</blockquote>
<br>
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