[RFC] Event timers on MIPS

[M. Warner Losh]

In message: <4C41A248.8090605 at FreeBSD.org>
            Alexander Motin <mav at FreeBSD.org> writes:
: Hi.
: 
: I've made a patch, updating MIPS timer code (except RMI) to utilize new
: MI event timer infrastructure. I've successfully built QEMU and XLR
: kernels with the patch. Unluckily I can't test how it works, unless
: somebody teach me how to cook QEMU to run it. I also haven't ported RMI
: timers drivers, as I am not sure how that hardware is intended to work.
: 
: Patch for HEAD can be found here:
: http://people.freebsd.org/~mav/timers_mips.patch

I'll have to take a look at things.  On MIPS, the COMPARE register is
per core, so you don't need to send an IPI if you are using that
hardware.  IPIs are a little expensive, IIRC, since they tend to have
bad cache effects and put extra pressure on the TLBs.

It wasn't clear from these patches if you are using one core to do the
signalling for all the others or not.  If so, that represents a bit of
a regression.  I'm also not sure about not having a per-cpu timer's
effect on performance on a 16 or 32 core MIPS box...

: Could somebody falimiar with MIPS review/test my patch and extend it to
: RMI hardware?

I see someone else has commented on that.

Warner