svn commit: r296880 - in head: share/man/man9 sys/kern sys/sys

[Julian Elischer]

On 16/03/2016 3:12 AM, Gleb Smirnoff wrote:
>    Ravi,
>
> On Mon, Mar 14, 2016 at 05:33:06PM -0700, Ravi Pokala wrote:
> R> To make sure I'm reading this correctly:
> R>
> R> (1) The sysctl operates on an opaque array of (uint64_t)s. The elements of the array are not individually accessible.
>
> On array of counter_u64_t. The elements are individually accessible of course,
> but not by this sysctl API.
>
> R> (2) Reading the sysctl populates each element of the userspace array by calling counter_u64_fetch() on the corresponding element of the kernelspace array.
>
> Right.
>
> R> (3) Writing the sysctl clears the kernelspace array by calling counter_u64_zero() on each element.
>
> Right.
>
but it is not atomic.  since the user process decides the time delay 
between a read and write (zero) there could be  a lot of missed counts 
if you are resetting to zero after each read. better to just read in a 
loop and not zero..
here are somethings I've wanted at various times:
   read/zero atomic
   read timestamp as part of imported struct. (because you really 
can't do accurate timing from user space, but knowing when the data 
was read is a good replacement).
  read a "mib" (for want of a better term)  for each set, giving 
individual field names.