From: Xavier Leroy <Xavier.Leroy@inria.fr>
To: Dmitry Bely <dmitry.bely@gmail.com>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] testers wanted for experimental SSE2 back-end
Date: Mon, 29 Mar 2010 18:49:27 +0200 [thread overview]
Message-ID: <4BB0DA17.6090002@inria.fr> (raw)
In-Reply-To: <90823c941003230158n5080b46apc7c7462aead3372d@mail.gmail.com>
Hello Dmitry,
>> This is a call for testers concerning an experimental OCaml compiler
>> back-end that uses SSE2 instructions for floating-point arithmetic.[...]
>
> I cannot provide any benchmark yet
Too bad :-( I got very little feedback to my call: just one data point
(thanks Gaetan). Perhaps most OCaml users interested in numerical
computations have switched to x86-64bits already? At any rate, given
such a lack of interest, this x86-32/SSE2 port isn't going to make it
into the OCaml distribution.
> but even not taking into account
> the better register organization there are at least two areas where
> SSE2 can outperform x87 significantly.
>
> 1. Float to integer conversion
> Is quite inefficient on x87 because you have to explicitly set and
> restore rounding mode.
Right. The mode change makes the conversion about 10x slower on x87
than on SSE2. Apparently, float->int conversion is uncommon is
numerical code, otherwise we'd observe bigger speedups on real
applications...
> 2. Float compare
> Does not set flags on x87 so
The SSE2 code is prettier than the x87 code, but this doesn't seem to
translate into a significant performance gain, in my limited testing.
> As for SSE2 backend presented I have some thoughts regarding the code
> (fast math functions via x87 are questionable,
Most x86-32bits C libraries implement sin(), cos(), etc with the x87
instructions, so I'm curious to know what you find objectionable here.
> optimization of floating compare etc.) Where to discuss that - just
> here or there is some entry in Mantis?
Why not start on this list? We'll move to private e-mail if the
discussion becomes too heated :-)
- Xavier Leroy
next prev parent reply other threads:[~2010-03-29 16:49 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-09 16:33 Xavier Leroy
2010-03-10 19:25 ` [Caml-list] " Mike Lin
2010-03-10 20:51 ` Will M. Farr
2010-03-11 8:42 ` Xavier Leroy
2010-03-13 16:10 ` Gaëtan DUBREIL
2010-03-23 8:58 ` Dmitry Bely
2010-03-23 9:07 ` Daniel Bünzli
2010-03-23 9:22 ` Dmitry Bely
2010-03-29 16:49 ` Xavier Leroy [this message]
2010-03-29 18:58 ` Dmitry Bely
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