Hi All, We recently upgraded a number of applications from LLVM 3.5.2 (old JIT) to LLVM 3.7.1 (MCJit). We made the minimum changes needed for the switch (no changes to the IR generated or the IR optimizations applied). The resulting code pass all tests (8000+). However the runtime performance dropped significantly: 30% to 40% for all applications. The applications I am talking about optimize airline rosters and pairings. LLVM is used for compiling high level business rules to efficient machine code. 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). We have triple checked and reviewed the changes we made from old JIT to MCJIt. We also tried different ways to optimize the IR. However all results indicate that the performance drop happens in the (black box) IR to machine code stage. 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? If you need more information, in order to understand the issue, please tell us so that we can provide you with more details. Thanks Morten
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. On Thu, Feb 4, 2016 at 7:00 PM, Morten Brodersen via llvm-dev < llvm-dev at lists.llvm.org> wrote:> Hi All, > > We recently upgraded a number of applications from LLVM 3.5.2 (old JIT) to > LLVM 3.7.1 (MCJit). > > We made the minimum changes needed for the switch (no changes to the IR > generated or the IR optimizations applied). > > The resulting code pass all tests (8000+). > > However the runtime performance dropped significantly: 30% to 40% for all > applications. > > The applications I am talking about optimize airline rosters and pairings. > LLVM is used for compiling high level business rules to efficient machine > code. > > 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). > > We have triple checked and reviewed the changes we made from old JIT to > MCJIt. We also tried different ways to optimize the IR. > > However all results indicate that the performance drop happens in the > (black box) IR to machine code stage. > > 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? > > If you need more information, in order to understand the issue, please > tell us so that we can provide you with more details. > > Thanks > Morten > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160204/2d3ff41b/attachment.html>
----- Original Message -----> From: "Keno Fischer via llvm-dev" <llvm-dev at lists.llvm.org> > To: "Morten Brodersen" <Morten.Brodersen at constrainttec.com> > Cc: "llvm-dev" <llvm-dev at lists.llvm.org> > Sent: Thursday, February 4, 2016 6:05:29 PM > Subject: Re: [llvm-dev] MCJit Runtine Performance > > > > 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.And maybe the register allocator? Are you using the greedy one or the linear one? Are there any other MI-level optimizations running? -Hal> > > On Thu, Feb 4, 2016 at 7:00 PM, Morten Brodersen via llvm-dev < > llvm-dev at lists.llvm.org > wrote: > > > Hi All, > > We recently upgraded a number of applications from LLVM 3.5.2 (old > JIT) to LLVM 3.7.1 (MCJit). > > We made the minimum changes needed for the switch (no changes to the > IR generated or the IR optimizations applied). > > The resulting code pass all tests (8000+). > > However the runtime performance dropped significantly: 30% to 40% for > all applications. > > The applications I am talking about optimize airline rosters and > pairings. LLVM is used for compiling high level business rules to > efficient machine code. > > 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). > > We have triple checked and reviewed the changes we made from old JIT > to MCJIt. We also tried different ways to optimize the IR. > > However all results indicate that the performance drop happens in the > (black box) IR to machine code stage. > > 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? > > If you need more information, in order to understand the issue, > please tell us so that we can provide you with more details. > > Thanks > Morten > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev > > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev >-- Hal Finkel Assistant Computational Scientist Leadership Computing Facility Argonne National Laboratory
Hi Keno, Thanks for the fast ISel suggestion. Here are the results (for a small but representational run): LLVM 3.5.2 (old JIT): 4m44s LLVM 3.7.1 (MCJit) no fast ISel: 7m31s LLVM 3.7.1 (MCJit) fast ISel: 7m39s So not much of a difference unfortunately. On 05/02/16 11:05, Keno Fischer wrote:> 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. > > On Thu, Feb 4, 2016 at 7:00 PM, Morten Brodersen via llvm-dev > <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote: > > Hi All, > > We recently upgraded a number of applications from LLVM 3.5.2 (old > JIT) to LLVM 3.7.1 (MCJit). > > We made the minimum changes needed for the switch (no changes to > the IR generated or the IR optimizations applied). > > The resulting code pass all tests (8000+). > > However the runtime performance dropped significantly: 30% to 40% > for all applications. > > The applications I am talking about optimize airline rosters and > pairings. LLVM is used for compiling high level business rules to > efficient machine code. > > 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). > > We have triple checked and reviewed the changes we made from old > JIT to MCJIt. We also tried different ways to optimize the IR. > > However all results indicate that the performance drop happens in > the (black box) IR to machine code stage. > > 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? > > If you need more information, in order to understand the issue, > please tell us so that we can provide you with more details. > > Thanks > Morten > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev > >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160205/a8a4ab13/attachment.html>