Re: [dpdk-dev] Retrieving lcore worker thread id

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 15 Jul 2020 10:17:09 +0000
Mattias Rönnblom <mattias.ronnblom@ericsson.com> wrote:

> On 2020-07-14 22:51, Stephen Hemminger wrote:
> > On Tue, 14 Jul 2020 18:59:59 +0000
> > Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com> wrote:
> >  
> >> <snip>
> >>  
> >>>> Hi.  
> >>> Hey,
> >>>      
> >>>> In DPDK 19.11, the lcore_config struct of <rte_lcore.h> is made
> >>>> private, and with it the possibility to look up the thread id of the
> >>>> lcore worker threads disappears.
> >>>>
> >>>> One use case is an application with a monitoring function (on some
> >>>> control plane thread), which uses the thread ids to make sure the
> >>>> worker threads gets the CPU runtime they should, and thus is able to
> >>>> detect stalls.  
> >> This sounds similar to 'keep alive' functionality.
> >>  
> >>>> Is there some other way of finding out the thread_id of a lcore worker
> >>>> thread? All I can think of are hacks like using a temporary service
> >>>> function for service cores, in combination with requiring launched
> >>>> application threads also to store their thread id in some global
> >>>> structure (index by lcore_id).  
> >>> -1 for the service cores idea. I like the creative solution thinking, but not as a
> >>> long-term solution.
> >>>      
> >>>> Is there some cleaner way? If not, would adding something like a
> >>>> rte_lcore_thread_id() function make sense?  
> >> I guess here you mean the OS provided thread ID. Are there OS calls that provide the CPU runtime?  
> > This might be difficult sinc thread id in Linux/glibc is intentionally and opaque value.
> > According to Posix the only valid way to look at it is to use return value from
> > pthread_create() and pthread_self().
> >  
> 
> The rte_lcore_thread_id() would return this value, which could 
> subsequently be used in the application, calling pthread_getcpuclockid() 
> and clock_gettime() to retrieve the run time for the lcore worker 
> thread. No need to break the opacity in this case, although the Linux 
> thread id (i.e. the result of a gettid()) would be useful in case you 
> would want to dig around in /proc for other scheduler statistics.
> 
> 
> Regards,
> 
>      Mattias
> 

The issue is glibc doesn't want to allow gettid()
there is no wrapper, the only way to get it is using syscall()