Re: [Discuss-gnuradio] FIFO latency

[Alexander Chemeris]

On Mon, May 30, 2011 at 12:54, Andre Puschmann
<address@hidden> wrote:
> On 05/29/2011 10:22 AM, Alexander Chemeris wrote:
>> On Sun, May 29, 2011 at 03:05, Marcus D. Leech <address@hidden> wrote:
>>> On 05/28/2011 04:28 PM, Alexander Chemeris wrote:
>>>>>
>>>>> So, while this method is simple and good for non-realtime
>>>>> applications, it doesn't fit our needs. It may be usable for PHY<->MAC
>>>>> interaction, but even here I'm not sure it would work well.
>>>>>
>>>>> PS I test on Core 2 Duo 1.6 GHz with all the GUI stuff running.
>>>>
>>>> Ok, setting CPU affinity and cutting off startup artifacts definitely
>>>> helps.
>>>> Results are in attachment.
>>>> Still you can see quite some uncertainty.
>>>>
>>> OK, so a roughly 3:1 improvement in peak latency, and somewhat better
>>> predicability.
>>>
>>> But I'd still counter-assert, to your assertion, that latencies in the
>>> 10s-of-usec are entirely acceptable for
>>>  a wide-range of "real-time" applications, even with occasional latency
>>> excursions that increase the variability
>>>  by 50:1 or so.
>>>
>>> I can well imagine that they aren't acceptable for *your* application.  I
>>> mean, if all applications were the same, it would
>>>  be a very boring world, with most of us working at fast-food restaurants
>>> :-)
>>>
>>> But I'll stand by my original suggestion that use of FIFOs are an acceptable
>>> technique for a wide variety of applications, including
>>>  "real-time" applications, depending on constraints and requirements.
>>
>> Sure, I don't say that no one should use queues :)
>> I just want to say that it may not be suitable for applications with
>> more tight requirements - i.e. some alternative may be needed.
>>
>> But to say truth - I'm surprised by their performance, I thought it
>> would be much worse. So it may be a good starting point from which we
>> could refine later.
>>
>
> Linux' pipe implementation is known to be quite slow. I would suggest to
> use UNIX sockets instead. They should perform much better in terms of
> latency and performance.

Good idea.

-- 
Regards,
Alexander Chemeris.