[RFC] Event timers on sparc64/sun4v

[Alexander Motin]

Marius Strobl wrote:
> please don't commit this as-is:
> - using the stick instead of the tick counter for machines with CPUs
>   and thus tick counters running at different speeds has turned out
>   to be suboptimal, probably due to the fact that the 12.5MHz the
>   stick counters typically are driven by don't provide sufficient
>   granularity. Thus the more desireable variant for these machines
>   probably is to provide the tick counter of the BSP as the only
>   non-per-CPU timer and forward it to the APs via IPIs. This also
>   leaves the stick counter of all >= US-III machines generally
>   available for driving statclock, which likely is also desirable.
> - I'd like to keep the tick grace check as this caused problems in
>   the past. Probably tick_et_start() just should return an error
>   in this case.
> - I don't like wasting CPU cycles for determining whether the
>   workaround for BlackBird CPUs is needed (assuming #1 above is
>   implemented so distinguishing stick/tick is no longer needed)
>   with every (s)tick interrupt which are a lot as this just won't
>   ever change during runtime, i.e. I'd like to keep the different
>   interrupt handlers which are set up as needed.
> - Replacing intr_disable_all() with intr_disable() on sun4v
>   probably isn't a good idea as the latter doesn't disable IPIs
>   as it does on sparc64 and other architectures.

Here is new path, updated respecting two last points:
http://people.freebsd.org/~mav/timers_sparc2.patch

Don't you have some spare system with stick problems, so I could play
with it? And some documentation? I am curious, what is wrong there. :)

-- 
Alexander Motin