GHC 8.4.1-rc1 is slower on a ray-tracer project

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GHC 8.4.1-rc1 is slower on a ray-tracer project

varosi
Hello!

I have a small ray-tracer project: https://bitbucket.org/varosi/cgraytrace
From time to time I'm testing it with different GHC versions including ARM.

Yesterday I successfully compiled it with GHC 8.4.1-rc1. I got compiled it with 8.2.2 and 8.0.2 as well and ran tests for about a minute each on my Intel Core i7 machine on Windows 10 x64.

I got this results:

GHC 8.4.1-rc1 
Average time: 61.87s

GHC 8.2.2
Average time: 60.09s

GHC 8.0.2
Average time: 67.07s

Application is doing multi-threaded brute-force ray-tracing with GI, so a lot of rays are shot around.
It seems that previous GHC 8.2.2 is doing better on a high-performance application. I know that this test is too simple, but it is on a real world problem and application and not one for whole purpose of benchmarking.

Any thoughts are welcome!

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Re: GHC 8.4.1-rc1 is slower on a ray-tracer project

Ben Gamari-3
Vassil Ognyanov Keremidchiev <[hidden email]> writes:

> Hello!
>
> I have a small ray-tracer project: https://bitbucket.org/varosi/cgraytrace
> From time to time I'm testing it with different GHC versions including ARM.
>
Thanks for doing these tests! I have opened #14870 to make sure we don't
lose track of this. It would be interesting to bisect this to see where
we went off the rails.

This is a very interesting example which the Cabal file says is in the
public domain. In principle it would be a nice case to include in nofib,
although I suspect it has few too many dependencies.

Cheers,

- Ben


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Re: GHC 8.4.1-rc1 is slower on a ray-tracer project

David Feuer
I don't see how 62 seconds rather than 60 is anything close to going off the rails. Did I read something wrong? This sounds more like a minor wibble.

On Feb 28, 2018 10:32 AM, "Ben Gamari" <[hidden email]> wrote:
Vassil Ognyanov Keremidchiev <[hidden email]> writes:

> Hello!
>
> I have a small ray-tracer project: https://bitbucket.org/varosi/cgraytrace
> From time to time I'm testing it with different GHC versions including ARM.
>
Thanks for doing these tests! I have opened #14870 to make sure we don't
lose track of this. It would be interesting to bisect this to see where
we went off the rails.

This is a very interesting example which the Cabal file says is in the
public domain. In principle it would be a nice case to include in nofib,
although I suspect it has few too many dependencies.

Cheers,

- Ben


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Re: GHC 8.4.1-rc1 is slower on a ray-tracer project

varosi
Those numbers are averaged from 5-10 runs. So there is some slow down for some reason. It's not great and it's just 3%. But I hoped that 8.4 has more optimizations and will lead to better performance and not worse.

2018-02-28 17:47 GMT+02:00 David Feuer <[hidden email]>:
I don't see how 62 seconds rather than 60 is anything close to going off the rails. Did I read something wrong? This sounds more like a minor wibble.

On Feb 28, 2018 10:32 AM, "Ben Gamari" <[hidden email]> wrote:
Vassil Ognyanov Keremidchiev <[hidden email]> writes:

> Hello!
>
> I have a small ray-tracer project: https://bitbucket.org/varosi/cgraytrace
> From time to time I'm testing it with different GHC versions including ARM.
>
Thanks for doing these tests! I have opened #14870 to make sure we don't
lose track of this. It would be interesting to bisect this to see where
we went off the rails.

This is a very interesting example which the Cabal file says is in the
public domain. In principle it would be a nice case to include in nofib,
although I suspect it has few too many dependencies.

Cheers,

- Ben


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Re: GHC 8.4.1-rc1 is slower on a ray-tracer project

varosi
The project could be stripped off yesod package which bring a lot dependencies with it. In cgraytrace-exe I don't use Yesod at all.

2018-02-28 19:22 GMT+02:00 Vassil Ognyanov Keremidchiev <[hidden email]>:
Those numbers are averaged from 5-10 runs. So there is some slow down for some reason. It's not great and it's just 3%. But I hoped that 8.4 has more optimizations and will lead to better performance and not worse.

2018-02-28 17:47 GMT+02:00 David Feuer <[hidden email]>:
I don't see how 62 seconds rather than 60 is anything close to going off the rails. Did I read something wrong? This sounds more like a minor wibble.

On Feb 28, 2018 10:32 AM, "Ben Gamari" <[hidden email]> wrote:
Vassil Ognyanov Keremidchiev <[hidden email]> writes:

> Hello!
>
> I have a small ray-tracer project: https://bitbucket.org/varosi/cgraytrace
> From time to time I'm testing it with different GHC versions including ARM.
>
Thanks for doing these tests! I have opened #14870 to make sure we don't
lose track of this. It would be interesting to bisect this to see where
we went off the rails.

This is a very interesting example which the Cabal file says is in the
public domain. In principle it would be a nice case to include in nofib,
although I suspect it has few too many dependencies.

Cheers,

- Ben


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Re: GHC 8.4.1-rc1 is slower on a ray-tracer project

Ben Gamari-3
In reply to this post by David Feuer
David Feuer <[hidden email]> writes:

> I don't see how 62 seconds rather than 60 is anything close to going off
> the rails. Did I read something wrong? This sounds more like a minor wibble.
>
"Off the rails" was a rhetorical flourish; indeed a single program
regressing by 3% isn't a catastrophe.

That being said, runtime performance improvements are hard-won prizes.
Consider that the largest allocations improvement arising from the
"Compiling without Continuations" paper was ~8%. Consequently, if
someone comes along with a 3% regression we would remiss not to
take it seriously.

Cheers,

- Ben


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