Re: cpuid_t typedef? (was Re: Processor cores not properly detected/activated?)

On Thursday, May 29, 2014 4:05:49 pm Adrian Chadd wrote:
> On 29 May 2014 11:44, John Baldwin <jhb_at_freebsd.org> wrote:
> > On Thursday, May 29, 2014 2:24:45 pm Adrian Chadd wrote:
> >> On 29 May 2014 10:18, John Baldwin <jhb_at_freebsd.org> wrote:
> >>
> >> >> > It costs wired memory to increase it for the kernel.  The userland set size
> >> >> > can be increased rather arbitrarily, so we don't need to make it but so large
> >> >> > as it is easy to bump later (even with a branch).
> >> >>
> >> >> Well, what about making the API/KBI use cpuset_t pointers for things
> >> >> rather than including it as a bitmask? Do you think there'd be a
> >> >> noticable performance overhead for the bits where it's indirecting
> >> >> through a pointer to get to the bitmask data?
> >> >
> >> > The wired memory is not due to cpuset_t.  The wired memory usage is due to things
> >> > that do 'struct foo foo_bits[MAXCPU]'.  The KBI issues I mentioned above are
> >> > 'struct rmlock' (so now you want any rmlock users to malloc space, or you
> >> > want rmlock_init() call malloc?  (that seems like a bad idea)).  The other one
> >> > is smp_rendezvous.  Plus, it's not just a pointer, you really need a (pointer,
> >> > size_t) tuple similar to what cpuset_getaffinity(), etc. use.
> >>
> >> Why would calling malloc be a problem? Except for the initial setup of
> >> things, anything dynamically allocating structs with embedded things
> >> like rmlocks are already dynamically allocating them via malloc or
> >> uma.
> >>
> >> There's a larger fundamental problem with malloc, fragmentation and
> >> getting the required larger allocations for things. But even a 4096
> >> CPU box would require a 512 byte malloc. That shouldn't be that hard
> >> to do. It'd just be from some memory that isn't close to the rest of
> >> the lock state.
> >
> > Other similar APIs like mtx_init() don't call malloc(), so it would be
> > unusual behavior.  However, we have several other problems before we can
> > move beyond 256 anyway (like pf).
> 
> Maybe behaviour has to change over time. :(
> 
> anyway. Besides all of this - I'm thinking of just introducing:
> 
> typedef uint32_t cpuid_t;
> 
> .. then once we've converted all the users, we can make NOCPU
> something other than 255 (which is the other limiting factor here..)
> 
> Any objections?

This one is a bit harder as you'll have to do shims for kinfo_proc, but
I think this is fine.  You could also just use u_int, but a new foo_t
isn't that bad I guess.

-- 
John Baldwin