Re: [Discuss-gnuradio] FIFO latency

[Andre Puschmann]

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.

Cheers,
Andre