Re: [Discuss-gnuradio] Non-deterministic behavior in GNU Radio

It depends on which box I look at.

1) volk_32fc_x2_divide_32fc a_avx u_sse3

2) volk_32fc_x2_divide_32fc a_avx u_avx

Ron

On 10/03/2018 08:05 AM, Müller, Marcus (CEL) wrote:
> Well, I'd be willing to call that a bug, all in all:
>
> Though I totally get the "machine accuracy" argument, I'd at least
> expect the same results when running the same program twice, on the
> same machine.
>
> Now, I'm an author of one of the 32fc_x2_divide_32fc implementations;
> I'd like to know what I can do to fix this. Ron, what was the machine
> that volk_profile picked for you?
>
> By the way, just as for the float/char (and other ints) conversion
> kernels, it's not inherently obvious who's right or wrong, the
> optimized or the generic impl. So, we should be analyzing which values
> led to the differing result.
>
> Best regards,
> Marcus
>
> On Wed, 2018-10-03 at 06:52 -0700, Ron Economos wrote:
>> That's the problem. If a set_output_multiple(4) in added to the
>> constructor in divide_cc_impl.cc, it solves the issue.
>>
>> Ron
>>
>> On 10/03/2018 06:42 AM, Ron Economos wrote:
>>> Well, I guess it's not really a bug. Most likely it has to do with the
>>> accuracy difference between the x86 intrinsics and the C library. If
>>> you look at the code in volk_32fc_x2_divide_32fc.h, the remaining
>>> points that are not a multiple of four are calculated with the C
>>> library. If the points from one run that are calculated with the C
>>> library line up with points calculated with intrinsics in the next
>>> run, there can be a mismatch.
>>>
>>> Ron
>>>
>>> On 10/03/2018 06:27 AM, Ron Economos wrote:
>>>> It's a VOLK bug. Go into ~/.volk/volk_profile and change the
>>>> volk_32fc_x2_divide_32fc line to generic. That fixes the issue here.
>>>>
>>>> Ron
>>>>
>>>>
>>>> On 10/03/2018 05:46 AM, Piotr Krysik wrote:
>>>>> Hi all,
>>>>>
>>>>> I simplified the flowgraph a bit and prepared a script that runs it
>>>>> twice and compares the results.
>>>>>
>>>>> https://imgur.com/a/CSjOeLc
>>>>>
>>>>> In short something is wrong indeed.
>>>>> Almost after every run of the script I get results with differences.
>>>>>
>>>>> I tested it on GNU Radio 3.7.12.0, I'm compiling the most fresh
>>>>> version
>>>>> now.
>>>>>
>>>>> Best Regards,
>>>>> Piotr Krysik
>>>>>
>>>>> W dniu 03.10.2018 o 06:55, Reiichiro Nakano pisze:
>>>>>> Here's an updated flowgraph where you don't need a separate file
>>>>>> source. Just run the flowgraph twice for a few seconds each. You'll
>>>>>> likely get different file sizes but `cmp` doesn't care, it'll still
>>>>>> show the first differing byte which should still prove the bug exists.

_______________________________________________
Discuss-gnuradio mailing list
Discuss-gnuradio@gnu.org
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio