[llvm-dev] Enable vectorizer-maximize-bandwidth by default?

[Dehao Chen via llvm-dev]

Thanks for the testcase. Could you add some more details about the
regression?

* How to build/run the testcase to reproduce the degradation?
* Is the degradation only exist in ATOM/SLM arch? If yes, could you help
analyze why maximize the bandwidth would make performance worse (as we do
not have these arches to run the perf tests).

Thanks,
Dehao

On Thu, Jun 1, 2017 at 6:12 AM, Agabaria, Mohammed <
mohammed.agabaria at intel.com> wrote:

> Attached the first reproducer of the Atom\SLM arch. degradation.  (~70%
> degradation).
>
> Chandler, those are part of EEMBC benchmarks.
>
>
>
> *From:* Chandler Carruth [mailto:chandlerc at gmail.com]
> *Sent:* Tuesday, May 30, 2017 23:07
> *To:* Agabaria, Mohammed <mohammed.agabaria at intel.com>; Flamedoge <
> code.kchoi at gmail.com>; Dehao Chen <dehao at google.com>
>
> *Cc:* llvm-dev <llvm-dev at lists.llvm.org>
> *Subject:* Re: [llvm-dev] Enable vectorizer-maximize-bandwidth by default?
>
>
>
> On Tue, May 30, 2017 at 1:40 AM Agabaria, Mohammed via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> We’re seeing nice improvements but also significant degradations on IA,
> which we would like to investigate before the patch is committed.
>
>
>
> Major degradations we see:
>
>
>
> networking
>
>    ip_pktcheckb1m          -6.80 %
>
>    ip_pktcheckb2m          -6.74 %
>
>    ip_pktcheckb4m          -7.57 %
>
>    ip_pktcheckb512k       -6.58 %
>
> Telecom
>
>    autcor00data_1          -78.02 %
>
>    autcor00data_2          -76.80 %
>
>    autcor00data_3          -77.00 %
>
> (on Atom)
>
>
>
> We still working on creating reproducers.
>
> In general we support this patch, just want to have a chance to
> investigate the issues. We need a few days for that.
>
>
>
> I mean, OK... but keep in mind that Dehao's original email went out over a
> week ago, so this patch has already been held up a while. As these
> benchmarks aren't readily available, we also can't do anything to help
> until a test case is posted.
>
>
>
> Have you considered contributing these benchmarks to the LLVM test suite?
>
>
>
>
>
>
>
>
>
> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org
> <llvm-dev-bounces at lists.llvm.org>] *On Behalf Of *Chandler Carruth via
> llvm-dev
> *Sent:* Tuesday, May 30, 2017 11:27
> *To:* Flamedoge <code.kchoi at gmail.com>; Dehao Chen <dehao at google.com>
> *Cc:* llvm-dev <llvm-dev at lists.llvm.org>
> *Subject:* Re: [llvm-dev] Enable vectorizer-maximize-bandwidth by default?
>
>
>
> If you care about such hardware, please run benchmarks with the flag?
>
>
>
> Dehao has made this flag available. It is important that those who care
> about particular hardware provid ebenchmark results. Not everyone in the
> community will have access to particular hardware variants.
>
>
>
> On Tue, May 30, 2017 at 1:14 AM Flamedoge <code.kchoi at gmail.com> wrote:
>
> Thank you for running these.
>
>
>
> May I suggest testing on AVX2 capable hardware? That would be Intel
> Haswell, AMD Carrizo and up.
>
> I'm not sure what "vectorizer-maximize-bandwidth" implies, but doubling
> the vector lanes may help light up parallel regions.
>
>
>
> Kevin
>
>
>
> On Tue, May 30, 2017 at 12:58 AM, Chandler Carruth via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> On Fri, May 19, 2017 at 4:01 PM Adam Nemet via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> I will run it on Cyclone/AArch64 next week.
>
>
>
> FYI, we're still waiting on these Adam...
>
>
>
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