Re: [Discuss-gnuradio] FIFO latency

[Josh Blum]

Just want to throw this out there because it seems relevant:
http://gnuradio.org/cgit/jblum.git/tree/gruel/src/include/gruel/high_res_timer.h?h=wip/high_res_timer&id=71b911d28a391ad0c67540e3658a6680d7449e1f

On 05/28/2011 02:42 PM, Alexander Chemeris wrote:
> On Sat, May 28, 2011 at 22:06, Marcus D. Leech <address@hidden> wrote:
>> I evaluated latency of a FIFO (actually an ordinary pipe, but the kernel
>> mechanisms are identical), and measured 30usecs average on my
>>  1.2GHz AMD Phenom system with plenty 'o memory.
>>
>> I sent timestamps across the FIFO (struct timeval), and the reader grabbed
>> the local time of day, and computed the difference.  There's
>>  a fair amount of uncertainty on the reader due to gettimeofday() call
>> overhead.  But 30usec on a wimpy CPU is certainly comfortably
>>  below 1msec.
> 
> gettimeofday() is a fast function. But if you want real high-fidelity
> - read CPU clock counter. Just make sure your app runs on a one
> selected core.
> 
> Could you post your app and raw results? I'm interested in
> min/mean/max values and distribution graphs. Because max values do
> play role when playing with real-time.
>