Re: [Qemu-devel] [PATCH v4 00/22] re-factor softfloat and add fp16 functions

["Alex Bennée" <alex.bennee@linaro.org>]

Peter Maydell <peter.maydell@linaro.org> writes:

> On 6 February 2018 at 16:47, Alex Bennée <alex.bennee@linaro.org> wrote:
>> Hi,
>>
>> The main change is applying the __attribute__((flatten)) to some of
>> the public functions that show up in Emilio's dbt-benchmark. This
>> seems to be a cleaner solution that squashing inlines higher up the
>> chain and still leaves the chance for re-use for the less widely used
>> functions. The results are an improvement over v3 by some margin:
>>
>>                          NBench score; higher is better
>>
>>     5 +-+-----------+-------------+------------+-------------+-----------+-+
>>       |                     ****### %%%%  +++                              |
>>   4.5 +-+...................*..*..#.%..%..****##..%%%%+ system-2.5       +-+
>>       |                     *  *  # %  %  *  * #  %  %      master         |
>>     4 +-+...................*..*..#.%..%..*..*.#..%..%softfloat-v3       +-+
>>   3.5 +-+...................*..*..#.%..%..*..*.#..%..%softfloat-%%%%.....+-+
>>       |                     *  *  # %  %  *  * #  %  %  * *  #  %  %       |
>>     3 +-+...................*..*..#.%..%..*..*.#..%..%..*.*..#..%..%.....+-+
>>       |                     *  *  #+%  %  *  * #$$$  %  * *  #  %  %       |
>>   2.5 +-+........####.......*..*..#$$..%..*..*.#..$..%..*.*..#..%..%.....+-+
>>       |       ****  #  %%%  *  *  # $  %  *  * #  $  %  * *  #$$$  %       |
>>     2 +-+.....*..*..#..%.%..*..*..#.$..%..*..*.#..$..%..*.*..#..$..%.....+-+
>>       |       *  *  #  % %  *  *  # $  %  *  * #  $  %  * *  #  $  %       |
>>   1.5 +-+.....*..*..#$$$.%..*..*..#.$..%..*..*.#..$..%..*.*..#..$..%.....+-+
>>     1 +-+.....*..*..#..$.%..*..*..#.$..%..*..*.#..$..%..*.*..#..$..%.....+-+
>>       |       *  *  #  $ %  *  *  # $  %  *  * #  $  %  * *  #  $  %       |
>>   0.5 +-+.....*..*..#..$.%..*..*..#.$..%..*..*.#..$..%..*.*..#..$..%.....+-+
>>       |       *  *  #  $ %  *  *  # $  %  *  * #  $  %  * *  #  $  %       |
>>     0 +-+-----****###$$$%%--****###$$%%%--****##$$$%%%--***###$$$%%%-----+-+
>>                  FOURIER     NEURAL NETLU DECOMPOSITION    gmean
>>
>> Slightly easier to read PNG:
>>
>>     https://i.imgur.com/XEeL0bC.png
>>
>> I think it's pretty ready for a merge. Shall I submit a pull myself or
>> does it make sense going via someone else? According to MAINTAINERS
>> Peter and Aurelien are responsible for this code...
>>
>> Alex Bennée (22):
>>   fpu/softfloat: implement float16_squash_input_denormal
>>   include/fpu/softfloat: remove USE_SOFTFLOAT_STRUCT_TYPES
>>   fpu/softfloat-types: new header to prevent excessive re-builds
>>   target/*/cpu.h: remove softfloat.h
>>   include/fpu/softfloat: implement float16_abs helper
>>   include/fpu/softfloat: implement float16_chs helper
>>   include/fpu/softfloat: implement float16_set_sign helper
>>   include/fpu/softfloat: add some float16 constants
>>   fpu/softfloat: improve comments on ARM NaN propagation
>>   fpu/softfloat: move the extract functions to the top of the file
>>   fpu/softfloat: define decompose structures
>>   fpu/softfloat: re-factor add/sub
>>   fpu/softfloat: re-factor mul
>>   fpu/softfloat: re-factor div
>>   fpu/softfloat: re-factor muladd
>>   fpu/softfloat: re-factor round_to_int
>>   fpu/softfloat: re-factor float to int/uint
>>   fpu/softfloat: re-factor int/uint to float
>>   fpu/softfloat: re-factor scalbn
>>   fpu/softfloat: re-factor minmax
>>   fpu/softfloat: re-factor compare
>>   fpu/softfloat: re-factor sqrt
>
> If you persuade git to use the --minimal, --patience or --histogram
> git diff option when generating these patches you'll find that it
> doesn't produce unreadable patches that provoke all the checkpatch
> warnings.

I think this is patchew getting confused as I generated the patches
with:

  [diff]
        algorithm = minimal

In my qemu.git/.git/config

> That in turn will let you find the genuine warning that
> got lost in all the spurious ones:
>
> Checking PATCH 16/22: fpu/softfloat: re-factor round_to_int...
> WARNING: line over 80 characters
> #127: FILE: fpu/softfloat.c:1261:
> +                inc = ((a.frac & roundeven_mask) != frac_lsbm1 ?
> frac_lsbm1 : 0);

Yeah that was in the release but the one character over is the ; and it
seemed nicer keeping all the logic on the same line.

> As far as I can tell from a quick search, the 'histogram'
> algorithm is reckoned to be about as fast as the default but
> much less likely to produce terrible diffs.
>
>   git config --global diff.algorithm histogram
>
> should set it up as the default for all diff-producing purposes
> including generating patches for email.
>
> thanks
> -- PMM


--
Alex Bennée