[llvm-dev] Buildbots timing out on full builds

David Blaikie via llvm-dev
Wed, 24 May 2017 16:31:57 -0000

On Tue, May 23, 2017 at 10:51 AM Daniel Sanders via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Could you give https://reviews.llvm.org/differential/diff/99949/ a try?
> It brings back the reverted commit and fixes two significant compile-time
> issues. Assuming it works for you too, I'll finish off the patches and
post
> them individually.
>
> The first one removes the single-use lambdas in the generated code. These
> turn out to be _really_ expensive. Replacing them with equivalent gotos
> saves 11 million allocations (~57%) during the course of compiling
> AArch64InstructionSelector.cpp.o. The cumulative number of bytes allocated
> also drops by ~4GB (~36%).
>

(this is outside my wheelhouse, so just as an aside): Could you explain
further what aspect of the change was that saved allocations? Lambdas
themselves don't allocate memory (std::function of a stateful lambda may
allocate memory - but I didn't see any std::function in your change, though
I might've missed it), so I'm guessing it's something else/some
other
aspect of the code in/outside the lambdas and where it moved that changed
the allocation pattern?


>
> The second one is to split up the functions by the number of operands in
> the top-level instruction. This constrains the scale of the task the
> register allocator needs to deal with in X86InstructionSelection.cpp.o.
>
> On 22 May 2017, at 10:42, Diana Picus <diana.picus at linaro.org>
wrote:
>
> Nope, no sanitizers.
>
> On 22 May 2017 at 11:38, Daniel Sanders <daniel_l_sanders at
apple.com>
> wrote:
>
> Is that with -fsanitize=memory too?
>
> I'm currently building ToT with r303258 reverted. Once that's done
I'll
> commit the revert and start investigating fixes.
>
> On 22 May 2017, at 10:22, Diana Picus <diana.picus at linaro.org>
wrote:
>
> Hi Daniel,
>
> I did your experiment on a TK1 machine (same as the bots) and for r303258
> I get:
> real    18m28.882s
> user    35m37.091s
> sys     0m44.726s
>
> and for r303259:
> real    50m52.048s
> user    88m25.473s
> sys     0m46.548s
>
> If I can help investigate, please let me know, otherwise we can just
> try your fixes and see how they affect compilation time.
>
> Thanks,
> Diana
>
> On 22 May 2017 at 10:49, Daniel Sanders <daniel_l_sanders at
apple.com>
> wrote:
>
> r303341 is the re-commit of the r303259 which tripled the number of rules
> that can be imported into GlobalISel from SelectionDAG. A compile time
> regression is to be expected but when I looked into it I found it was ~25s
> on my machine for the whole incremental build rather than the ~12mins you
> are seeing. I'll take another look.
>
> I'm aware of a couple easy improvements we could make to the way the
> importer works. I was leaving them until we change it over to a state
> machine but the most obvious is to group rules by their top-level gMIR
> instruction. This would reduce the cost of the std::sort that handles the
> rule priorities in generating the source file and will also make it simpler
> for the compiler to compile it.
>
>
> On 21 May 2017, at 11:16, Vitaly Buka <vitalybuka at google.com>
wrote:
>
> It must be r303341, I commented on corresponding llvm-commits thread.
>
> On Fri, May 19, 2017 at 7:34 AM, Diana Picus via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>
>
> Ok, thanks. I'll try to do a bisect next week to see if I can find it.
>
> Cheers,
> Diana
>
> On 19 May 2017 at 16:29, Daniel Sanders <daniel_l_sanders at
apple.com>
> wrote:
>
>
> On 19 May 2017, at 14:54, Daniel Sanders via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>
> r303259 will have increased compile-time since it tripled the number of
> importable
> SelectionDAG rules but a quick measurement building the affected file:
>  ninja
>
>
lib/Target/<Target>/CMakeFiles/LLVM<Target>CodeGen.dir/<Target>InstructionSelector.cpp.o
> for both ARM and AArch64 didn't show a significant increase. I'll
check
> whether
> it made a different to linking.
>
>
> I don't think it's r303259. Starting with a fully built r303259,
then
> updating to r303258 and running 'ninja' gives me:
>       real    2m28.273s
>       user    13m23.171s
>       sys     0m47.725s
> then updating to r303259 and running 'ninja' again gives me:
>       real    2m19.052s
>       user    13m38.802s
>       sys     0m44.551s
>
> sanitizer-x86_64-linux-fast also timed out after one of my commits this
> morning.
>
> On 19 May 2017, at 14:14, Diana Picus <diana.picus at linaro.org>
wrote:
>
> Hi,
>
> We've noticed that recently some of our bots (mostly
> clang-cmake-armv7-a15 and clang-cmake-thumbv7-a15) started timing out
> whenever someone commits a change to TableGen:
>
> r303418:
> http://lab.llvm.org:8011/builders/clang-cmake-armv7-a15/builds/7268
> r303346:
> http://lab.llvm.org:8011/builders/clang-cmake-armv7-a15/builds/7242
> r303341:
> http://lab.llvm.org:8011/builders/clang-cmake-armv7-a15/builds/7239
> r303259:
> http://lab.llvm.org:8011/builders/clang-cmake-armv7-a15/builds/7198
>
> TableGen changes before that (I checked about 3-4 of them) don't have
> this problem:
> r303253:
> http://lab.llvm.org:8011/builders/clang-cmake-armv7-a15/builds/7197
>
> That one in particular actually finishes the whole build in 635s,
> which is only a bit over 50% of the timeout limit (1200s). So, between
> r303253 and now, something happened that made full builds
> significantly slower. Does anyone have any idea what that might have
> been? Also, has anyone noticed this on other bots?
>
> Thanks,
> Diana
>
>
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