Date: Thu, 29 May 2014 16:18:54 -0400 From: John Baldwin <jhb@freebsd.org> To: Adrian Chadd <adrian@freebsd.org> Cc: Attilio Rao <attilio@freebsd.org>, freebsd-current <freebsd-current@freebsd.org>, Jia-Shiun Li <jiashiun@gmail.com>, Alan Somers <asomers@freebsd.org>, Tim Bishop <tim-lists@bishnet.net> Subject: Re: cpuid_t typedef? (was Re: Processor cores not properly detected/activated?) Message-ID: <201405291618.55058.jhb@freebsd.org> In-Reply-To: <CAJ-VmonhjQZGhxTjgJA5a3Cyu%2Bx7HCmuK1MDoLQtdpHJ4wR-FA@mail.gmail.com> References: <CAJ-VmonhjQZGhxTjgJA5a3Cyu%2Bx7HCmuK1MDoLQtdpHJ4wR-FA@mail.gmail.com>
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On Thursday, May 29, 2014 4:05:49 pm Adrian Chadd wrote: > On 29 May 2014 11:44, John Baldwin <jhb@freebsd.org> wrote: > > On Thursday, May 29, 2014 2:24:45 pm Adrian Chadd wrote: > >> On 29 May 2014 10:18, John Baldwin <jhb@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
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