[dm-devel] [PATCH 2/4] dm stats: support precise timestamps

[Mikulas Patocka]

On Tue, 16 Jun 2015, Vivek Goyal wrote:

> On Tue, Jun 09, 2015 at 05:21:39PM -0400, Mikulas Patocka wrote:
> 
> [..]
> >  Messages
> >  ========
> >  
> > -    @stats_create <range> <step> [<program_id> [<aux_data>]]
> > +    @stats_create <range> <step>
> > +    		[<number_of_optional_arguments> <optional_arguments>...]
> > +		[<program_id> [<aux_data>]]
> >  
> >  	Create a new region and return the region_id.
> >  
> > @@ -48,6 +54,17 @@ Messages
> >  	  "/<number_of_areas>" - the range is subdivided into the specified
> >  				 number of areas.
> >  
> > +	<number_of_optional_arguments>
> > +	  The number of optional arguments
> > +
> > +	<optional_arguments>
> > +	  The following optional arguments are supported
> > +	  precise_timestamps - use precise timer with nanosecond resolution
> > +	  	instead of the "jiffies" variable.  When this argument is
> > +		used, the resulting times are in nanoseconds instead of
> > +		milliseconds.  Precise timestamps are a little bit slower
> > +		to obtain than jiffies-based timestamps.
> > +
> 
> Instead of "precise_timestams" will it make sense to call it
> "nanosecond_timestamps" or "ns_timestamps".
> 
> 
> >  	<program_id>
> >  	  An optional parameter.  A name that uniquely identifies
> >  	  the userspace owner of the range.  This groups ranges together
> 
> We are adding these new parameters/arguments in between existing parameters.
> Will it break any of the existing scritps. Will it make sense to add these
> new parameters at the end. It is more intuitive.

It could break someone who uses number as program_id - but there is no 
program on Linux with name that is a pure number.

We can't add it at the end because program_id and aux_data are already 
optional arguments.

> Also, I was wondering that why do we need to introduce this notion of
> number of optional arguments. Can't we just introduce another optional
> parameter [ns_timestamps]. That feels little simpler.

Then, it will clash with program_id "ns_timestamps". Device mapper uses 
this "number of optional arguments" notation at other places, so I used it 
too,

Mikulas

> Thanks
> Vivek