llvm dev - Aug 2014 - [LLVMdev] Recent compile time performance regressions

On 1 August 2014 21:33, Chandler Carruth <chandlerc at google.com>
wrote:
>> Note, this patch is actually the smaller culprit, around 209801 there
is
>> another performance regression, but I have no idea if/where this is
coming
>> from or if this for some reason is a false positive.
>
>
> I'm having to question the results on this bot. The range of commits
which
> cause the larger compile time regression is 209797 - 209799... But those
> commits are totally innocuous. The closest to a something that could go
> poorly would be r209798, but that commit doesn't seem plausible for a
huge
> slowdown.
>
> I wonder if there is something weird going on with the bot...
209797-209799 regression is false positive, due to reverting perf back
to original timeit tool.(r209797)

However the multithreading stuff is real regression and I'm able to
reproduce same regression on my local build bots.

-Yi

On 1 August 2014 21:47, Yi Kong <kongy.dev at gmail.com>
wrote:
> On 1 August 2014 21:33, Chandler Carruth <chandlerc at google.com>
wrote:
>>> Note, this patch is actually the smaller culprit, around 209801
there is
>>> another performance regression, but I have no idea if/where this is
coming
>>> from or if this for some reason is a false positive.
>>
>>
>> I'm having to question the results on this bot. The range of
commits which
>> cause the larger compile time regression is 209797 - 209799... But
those
>> commits are totally innocuous. The closest to a something that could go
>> poorly would be r209798, but that commit doesn't seem plausible for
a huge
>> slowdown.
>>
>> I wonder if there is something weird going on with the bot...
>
> 209797-209799 regression is false positive, due to reverting perf back
> to original timeit tool.(r209797)
I misread my own commit message.:(
It's turning perf back on.
>
> However the multithreading stuff is real regression and I'm able to
> reproduce same regression on my local build bots.
>
> -Yi

On Fri, Aug 1, 2014 at 1:47 PM, Yi Kong <kongy.dev at gmail.com> wrote:
> However the multithreading stuff is real regression and I'm able to
> reproduce same regression on my local build bots.
>
Can you share a preprocessed input and commandline which reproduces this
regression?
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Hi Chandler,

On an x86 system, for ToT LLVM:

With "Remove support for LLVM runtime multithreading": 23.8788
With patch reverted: 22.5229

That's around 6% regression.

Detailed JSON file is at http://paste.debian.net/113238,
http://paste.debian.net/113239

-Yi

On 1 August 2014 21:56, Chandler Carruth <chandlerc at google.com>
wrote:
>
> On Fri, Aug 1, 2014 at 1:47 PM, Yi Kong <kongy.dev at gmail.com>
wrote:
>>
>> However the multithreading stuff is real regression and I'm able to
>> reproduce same regression on my local build bots.
>
>
> Can you share a preprocessed input and commandline which reproduces this
> regression?