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Re: What *is* the API for sched_getaffinity? Should sched_getaffinity always succeed when using cpu_set_t?
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: Roland McGrath <roland at hack dot frob dot com>
- Cc: KOSAKI Motohiro <kosaki dot motohiro at gmail dot com>, libc-alpha <libc-alpha at sourceware dot org>
- Date: Mon, 22 Jul 2013 19:00:35 -0400
- Subject: Re: What *is* the API for sched_getaffinity? Should sched_getaffinity always succeed when using cpu_set_t?
- References: <51E42BFE dot 7000301 at redhat dot com> <51E4A0BB dot 2070802 at gmail dot com> <51E4A123 dot 9070001 at gmail dot com> <51E6F3ED dot 8000502 at redhat dot com> <51E6F956 dot 5050902 at gmail dot com> <51E714DE dot 6060802 at redhat dot com> <CAHGf_=oZW3kNA3V-9u+BZNs3tL3JKCsO2a0Q6f0iJzo=N4Wb8w at mail dot gmail dot com> <51E7B205 dot 3060905 at redhat dot com> <20130722214335 dot D9AFF2C06F at topped-with-meat dot com> <51EDB378 dot 8070301 at redhat dot com> <20130722224553 dot 933BA2C070 at topped-with-meat dot com>
On 07/22/2013 06:45 PM, Roland McGrath wrote:
> I have a hard time seeing why (b) would ever be useful.
> I think (c) was always the intended semantic of _SC_NPROCESSORS_CONF.
That's different than what we have implemented in glibc.
Why do you have a hard time seeing that (b) would be useful?
I see (b) being useful for:
* Detection of number of logical cpus that are in the
system vs. number that are online.
- Ask your admin to bring the rest of them online?
* Used to create a minimally sized structure to track
per-logical-CPU data.
- As it is implemented _SC_NPROCESSORS_CONF is a minimal
value. Fixing it to match your expected semantics e.g
making it the number of possible CPUs, is going
to make this value potentially much larger.
What use is there to knowing (c) except to choose to optimize
space vs. time and allocate sufficient resources to track all
possible cpus that system could have (only a reboot can change
this in linux right now)?
Comments?
Cheers,
Carlos.