Re: [dpdk-dev] [PATCH v3] distributor_app: new sample app

[Neil Horman <nhorman@tuxdriver.com>]

On Mon, Oct 06, 2014 at 02:16:22PM +0000, Pattan, Reshma wrote:
> 
> 
> > -----Original Message-----
> > From: Neil Horman [mailto:nhorman@tuxdriver.com]
> > Sent: Wednesday, October 1, 2014 5:08 PM
> > To: Richardson, Bruce
> > Cc: Pattan, Reshma; dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH v3] distributor_app: new sample app
> > 
> > > > >
> > > > > 1)I had sent v5 patch which handles graceful shutdown of rx and tx
> > > > > threads upon SIGINT
> > > > I see it and will take a look shortly, thanks.
> > > >
> > > > > 2)Worker thread graceful shutdown was not handled as of now as it needs
> > some change in lcore_worker logic , which will be done in future enhancements.
> > > > Not sure I understand what you mean here.  Can you elaborate?
> > > >
> rte_distributor_process which runs as part of rx thread will process incoming packets and checks for any requests for the packets from worker threads .
> If request is seen, it adds the packet/work  to particular workers back log and proceed with processing of  next packet.
>  If no request seen the packet index will not be incremented and the while loop which is conditionally based on packet indexing  runs in a continuous loop without breaking and rx thread will not proceed with next statement execution until unless rte_distributor_process  comes out of while loop. 
> This issue happens only when we enable graceful shutdown logic for both rx/worker threads, as workers threads gets killed and no request seen by rx thread and it stucks. 
> Hence as of now graceful shutdown logic is provided only for rx thread. For worker threads will check what can be done in next enhancements. 
> 
> Thanks,
> Reshma
> 

I see what you're saying, Once you make a call to rte_distributor_get_pkt, you
have no way to gracefully shut down use of the rte_distributor_library. Not just
this application, but any application.  Thats just not sane, and suggests that
we integrated the rte_distributor library too soon.  I would suggest that you
prefix this patch with an update to the rte distributor library to allow
rte_distributor_get_pkt and friends to return NULL if the queue is emtpy.
Applications should be checking the return value for NULL anyway, and can
preform the rte_pause operation.  Then update this patch to do a clean exit.  To
say that "we will check what can be done in the next enhancements" is to say
that this won't be addressed again until a paying custmoer gripes about it.
Neil

> > > > > 3)Freeing of mempool is also not handled , as the framework support is not
> > available.
> > > > Ew, I hadn't noticed that, freeing of mempools seems like something
> > > > we should implement.
> > > >
> > > > > 4)Cleaning of rx/tx queues not done, as it needs some extensive logic
> > which we haven't planned as of now. Will check the possibility of doing it in
> > future  enhancements    i.e in next version of sample application.
> > > > We can't just flush the queues after we shutdown the workers?  I
> > > > presume a queue flush operation exists, yes?
> > > > Neil
> > >
> > > Other than code hygiene, which does have some value in itself, I can't
> > > really see what the practical point of such cleanup would be.
> > >
> > This is really the only assertion I'm trying to make.  I understand this application
> > won't suffer from exiting uncleanly, and that makes the need for preforming
> > cleanup little more than overhead.
> > 
> > But that said, hygine is exactly the point I'm driving at here.  These are example
> > applications, that presumably people look at when writing their own apps.  If
> > you don't do things properly, people looking at your code are less likely to do
> > them as well.  Even if it doesn't hurt for you to exit uncleanly, it will hurt
> > someone, and if they look to these examples as a source of best practices, it
> > seems to me that it would be in everyones interest, if best practices were
> > demonstrated.
> > 
> > Neil
> 
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