[dpdk-dev] [RFC] Yet another option for DPDK options

Panu Matilainen pmatilai at redhat.com
Fri Jun 3 14:53:00 CEST 2016


On 06/03/2016 03:01 PM, Arnon Warshavsky wrote:
>
>
> On Fri, Jun 3, 2016 at 2:50 PM, Neil Horman <nhorman at tuxdriver.com
> <mailto:nhorman at tuxdriver.com>> wrote:
>
>     On Fri, Jun 03, 2016 at 12:01:30PM +0100, Bruce Richardson wrote:
>     > On Fri, Jun 03, 2016 at 11:29:43AM +0100, Bruce Richardson wrote:
>     > > On Thu, Jun 02, 2016 at 04:08:37PM -0400, Neil Horman wrote:
>     > > > On Thu, Jun 02, 2016 at 07:41:10PM +0000, Wiles, Keith wrote:
>     > > > >
>     > > > > On 6/2/16, 12:11 PM, "Neil Horman" <nhorman at tuxdriver.com
>     <mailto:nhorman at tuxdriver.com>> wrote:
>     > > > >
>     > > > > >
>     > > > > >1) The definition of a config structure that can be passed
>     to rte_eal_init,
>     > > > > >defining the configuration for that running process
>     > > > >
>     > > > > Having a configuration structure means we have to have an
>     ABI change to that structure anytime we add or remove an option. I
>     was thinking a very simple DB of some kind would be better. Have the
>     code query the DB to obtain the needed information. The APIs used to
>     query and set the DB needs to be very easy to use as well.
>     > > >
>     > > > Thats a fair point.  A decent starting point is likely a
>     simple struct that
>     > > > looks like this:
>     > > >
>     > > > struct key_vals {
>     > > >   char *key;
>     > > >   union {
>     > > >           ulong longval;
>     > > >           void *ptrval;
>     > > >   } value;
>     > > > };
>     > > >
>     > > > struct config {
>     > > >   size_t count;
>     > > >   struct key_vals kvp[0];
>     > > > };
>     > > >
>     > > > >
>     > > > > Maybe each option can define its own structure if needed or
>     just a simple variable type can be used for the basic types (int,
>     string, bool, …)
>     > > > >
>     > > > Well, if you have config sections that require mulitiple
>     elements, I'd handle
>     > > > that with naming, i.e. if you have a config group that has an
>     int and char
>     > > > value, I'd name them "group.intval", and "group.charval", so
>     they are
>     > > > independently searchable, but linked from a nomenclature
>     standpoint.
>     > > >
>     > > > > Would this work better in the long run, does a fixed
>     structure still make sense?
>     > > > >
>     > > > No. I think you're ABI concerns are valid, but the above is
>     likely a good
>     > > > starting point to address them.
>     > > >
>     > > > Best
>     > > > Neil
>     > >
>     > > I'll throw out one implementation idea here that I looked at
>     previously, for
>     > > the reason that it was simple enough implement with existing code.
>     > >
>     > > We already have the cfgfile library which works with name/value
>     pairs read from
>     > > ini files on disk. However, it would be easy enough to add
>     couple of APIs to
>     > > that to allow the user to "set" values inside an ini structure
>     as well. With
>     > > that done we can then just add a new eal_init api which takes a
>     single
>     > > "struct rte_cfgfile *" as parameter. For those apps that want to
>     just use
>     > > inifiles for configuration straight, they can then do:
>     > >
>     > > cfg = rte_cfgfile_load("my_cfg_file");
>     > > rte_eal_newinit(cfg);
>     > >
>     > > Those who want a different config can instead do:
>     > >
>     > > cfg = rte_cfgfile_new();
>     > > rte_cfgfile_add_section(cfg, "dpdk");
>     > > foreach_eal_setting_wanted:
>     > >     rte_cfgfile_set(cfg, "dpdk", mysetting, myvalue);
>     > > rte_eal_newinit(cfg);
>     > >
>     > From chatting to a couple of other DPDK dev's here I suspect I may
>     not have
>     > been entirely clear here with this example. What is being shown
>     above is building
>     > up a "config-file" in memory - or rather a config structure which
>     happens to
>     > have the idea of sections and values as an ini file has. There is
>     no actual
>     > file ever being written to disk, and for those using any non-ini
>     config file
>     > structure for their app, the code overhead of using the APIs above
>     should be
>     > pretty much the same as building up any other set of key-value
>     pairs in
>     > memory to pass to an init function.
>     >
>     > Hope this is a little clearer now.
>     >
>     I'm fine with the idea of reusing the config file library that
>     currently exists,
>     or more to the point, modifying it to be usable as a configuration
>     API, rather
>     than a configuration file parser.  My primary interest is in
>     separating the user
>     configuration mechanism from the internal library configuration lookup
>     mechanism.  What I would really like to be able to see is
>     application developers
>     have the flexibiilty to choose their own configuration method and
>     format, and
>     programatically build a configuration for the dpdk on a per-instance
>     basis prior
>     to calling rte_eal_init
>
>     It seems like this approach satisfies that requirement
>     Neil
>
>
> If the there is no configuration structure , rather an opaque
> configuration key/value store ,
> the user applications can set and get knobs that are not seen by anyone
> (library) that does not know them by name
>
> e.g
>
> int num_nodes = getCfgInt ( cfgObject , "eal" , "num_numa_nodes");
> int delay = getCfgInt ( cfgObject , "drivers.ixgbe" , "some_delay");
> setCfgInt (cfgObject , "my_app" , "num_days" , 7);
> setCfgString (cfgObject , "my_app" , "best_day" , "Wednesday");

I dont see why it would not be possible to have the libraries export 
their known config keys in one way or the other. Or more.

One aspect is runtime queries which would need an API of some kind. 
Being able to query default values should work for that purpose and be 
handy for various other uses as well.

Another one is build-time sanity checking which could be doen by 
auto-generating header(s) from the library known keys, eg

#define CFG_NUM_NUMA_NODES "num_numa_nodes"

so if you use the macro instead of the actual string, you'll get a 
compiler error in case of unknown key instead of runtime misbehavior in 
case of typoed values etc. Whether that's worth it is an entirely 
different question.

	- Panu -





> /Arnon
>



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