[CFR][CFT] counter(9): new API for faster and raceless counters

[Gary Palmer]

On Wed, Apr 03, 2013 at 01:26:07AM +0200, Pawel Jakub Dawidek wrote:
> On Mon, Apr 01, 2013 at 03:51:28PM +0400, Gleb Smirnoff wrote:
> >   Hi!
> > 
> >   Together with Konstantin Belousov (kib@) we developed a new API that is
> > initially purposed for (but not limited to) collecting statistical
> > data in kernel.
> 
> Is there any plan to implement universal way of exporting those
> statistics out of the kernel?
> 
> Solaris has a framework for in-kernel statistics, which are exported via
> kstat tool. For ZFS I export them via sysctl. If you have ZFS loaded you
> can try 'sysctl kstat'.
> 
> It would be nice for counter_u64_alloc() to take additional argument
> 'name' and to create sysctl for the counter automatically. We could then
> slowly start migrating userland tools to use sysctls (or some wrapper
> userland API), but we immediately make those statistics available for
> use in scripts.

Sorry for potentially turning this into a bikeshed, but is sysctl the
best interface for this?  It is great for scripts as the CLI is already
there, however it is not a bulk interface so grabbing all the ZFS
statistics takes quite a few trips through our system call handler - 438
on my 9.1 box for "sysctl kstat" (found via ktrace and then
kdump | grep -c SCTL), which is not ideal when there are only 87
stats there. (5 calls per OID returned and 3 initial calls to get set up)

I'm not sure I have a better alternative other than a geom style bulk
export via XML or some other format, however I wanted to raise it for
consideration.  I wouldn't hold up the checkin of the code for this,
however if another way of gathering the data is needed/desired then it
would be good to get it in before people get too used to the sysctl 
way.  


Thanks,

Gary