Date: Thu, 29 May 2014 13:18:35 -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: Processor cores not properly detected/activated? Message-ID: <201405291318.36130.jhb@freebsd.org> In-Reply-To: <CAJ-VmomzDWHTZ_En5PUGrse%2B3oFyXksPWB5OHx7_US_Or6vW6Q@mail.gmail.com> References: <20140524014713.GF13462@carrick-users.bishnet.net> <201405281358.35924.jhb@freebsd.org> <CAJ-VmomzDWHTZ_En5PUGrse%2B3oFyXksPWB5OHx7_US_Or6vW6Q@mail.gmail.com>
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On Thursday, May 29, 2014 12:53:54 pm Adrian Chadd wrote: > On 28 May 2014 10:58, John Baldwin <jhb@freebsd.org> wrote: > > On Wednesday, May 28, 2014 1:51:28 pm Adrian Chadd wrote: > >> On 28 May 2014 06:56, John Baldwin <jhb@freebsd.org> wrote: > >> > >> > >> > Userland cpusets only default to 128 (CPU_MAXSIZE in <sys/_cpuset.h>). > >> > Changing MAXCPU to even 128 is unfortunately a potential KBI change since it > >> > changes the size of 'cpuset_t'. We can certainly bump these in HEAD for 11, > >> > but we might not be able to MFC them without introducing ABI breakage. > >> > (The cpuset APIs do allow the size of cpuset_t to change as the size is > >> > encoded in the API calls, so there is that, it's more that if some public > >> > structure embeds a cpuset_t in the kernel that we would have problems. I > >> > thought 'struct pcpu' did, but it does not.) > >> > > >> > Hmm, smp_rendezvous() accepts a cpuset_t as its first argument (and is a > >> > public symbol used by kernel modules such as dtrace). 'struct rmlock' also > >> > embeds a cpuset_t. So, I think we can't bump cpuset_t without breaking > >> > the KBI. We can bump it in HEAD however. (Note, if re@ signed off, we could > >> > perhaps merge to 10, but we tend to be very hesitant about breaking the KBI.) > >> > One thing we could do safely is bump the userland cpuset size to 256 in 10. > >> > It's really only MAXCPU that is problematic. > >> > > >> > In particular, I propose we bump the userland cpuset_t size to 256 now (and > >> > go ahead and merge that to 10). In HEAD only we can bump MAXCPU for amd64 > >> > to 256. > >> > >> Since 11 is going to be around for a few years, can we experiment > >> bumping it up to something compute-cluster-computer-sized just to get > >> it over with? Something stupid, like 4096 or something? > > > > 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. -- John Baldwin
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