Date: Fri, 16 Mar 2018 16:50:56 +0100
From: Natanael Copa <ncopa@alpinelinux.org>
To: Steffen Nurpmeso <steffen@sdaoden.eu>
Cc: alpine-user@lists.alpinelinux.org
Subject: Re: [alpine-user] FYI: community/zstd binary much (up to 4x) slower
 than necessary
Message-ID: <20180316165056.7768bcf0@ncopa-desktop.copa.dup.pw>
In-Reply-To: <20180316153741.sbhOT%steffen@sdaoden.eu>
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On Fri, 16 Mar 2018 16:37:41 +0100
Steffen Nurpmeso <steffen@sdaoden.eu> wrote:

> Hello.
> 
> Natanael Copa <ncopa@alpinelinux.org> wrote:
>  |On Tue, 13 Mar 2018 19:06:48 +0100
>  |Steffen Nurpmeso <steffen@sdaoden.eu> wrote:
>  |
>  |> Hello, for your possible interest.
>  |>
>  |> In a thead for the LUGA(ustria) i eventually had to time some
>  |> compression algorithms and wondered why zstd is so slow, but
>  |> especially so the decompressing stage, which a key feature of this
>  |> one.  It turns out that the -Os compilation causes, well, drama-
>  |> tical performance degradation.  I compiled my own with -O3 and the
>  |> difference is up to factor four.  Just one example:  
>  ...
>  |Are you compressing the same file? I see x4.txt, x5.txt avs x1.txt.
>  |File content may make difference too.
> 
> Yes, it was all the same.  It was just an excerpt of that LUGA
> message, sorry.
> 
>  |> That makes me actually wonder how ports should deal with CFLAGS.
>  |> Is it acceptable for a port to watch for compiler flags and set
>  |> them, my MUA would go for PIE, relro and all that, then?  
>  |
>  |I think if the difference is 4x then, yes, I think we should explicitly
>  |set CFLAGS from aport with a reference on why. I do prefer -O2 over -O3
>  |though, so It would be nice to see the numbers with -O2 and also what
>  |the numbers are on different platforms.
>  |
>  |We already explicitly set -O2 for zlib, because its a case where we do
>  |want trade more speed at the cost of size.
> 
> I see.  I only have control of x86 (with Linux) for now, i really
> have to do something about that at some day...  With -O2:
> 
>   #?0[steffen@essex zstd]$ CFLAGS=-O2 make zstd
>   ...
>   #?0[steffen@essex zstd]$ ll zstd
>   -rwxr-x---    1 steffen  steffen     582392 Mar 16 16:11 zstd*

...

> 
> No difference with -O3, actually:
> 
>   #?0[steffen@essex zstd]$ CFLAGS=-O3 make zstd
>   ...
>   #?0[steffen@essex zstd]$ ll zstd
>   -rwxr-x---    1 steffen  steffen     619296 Mar 16 16:17 zstd*

Yes, no big difference in performance -O2 vs -O3, but it gets bigger.

...

> But lots of difference for /usr/bin/zstd:
> 
>   #?0[steffen@essex zstd]$ ll /usr/bin/zstd
>   -rwxr-xr-x    1 root     root        382792 Dec 27 15:17 /usr/bin/zstd*

I assume that is with -Os.

I think this alone is good enough reason to force -O2.

Thanks!

-nc


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