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Date: Thu, 28 Jun 2012 10:25:38 +0800
From: David Xu <listlog2011@gmail.com>
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To: Attilio Rao <attilio@freebsd.org>
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Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org,
	src-committers@freebsd.org,
	Konstantin Belousov <kib@freebsd.org>, davidxu@freebsd.org
Subject: Re: svn commit: r237660 - head/lib/libc/gen
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On 2012/6/28 10:21, Attilio Rao wrote:
> 2012/6/28, David Xu<listlog2011@gmail.com>:
>> On 2012/6/28 4:32, Konstantin Belousov wrote:
>>> Author: kib
>>> Date: Wed Jun 27 20:32:45 2012
>>> New Revision: 237660
>>> URL: http://svn.freebsd.org/changeset/base/237660
>>>
>>> Log:
>>>     Optimize the handling of SC_NPROCESSORS_CONF, by using auxv AT_NCPU
>>>     value if present.
>>>
>>>     MFC after:	1 week
>>>
>>> Modified:
>>>     head/lib/libc/gen/sysconf.c
>>>
>>> Modified: head/lib/libc/gen/sysconf.c
>>> ==============================================================================
>>> --- head/lib/libc/gen/sysconf.c	Wed Jun 27 20:24:25 2012	(r237659)
>>> +++ head/lib/libc/gen/sysconf.c	Wed Jun 27 20:32:45 2012	(r237660)
>>> @@ -42,6 +42,7 @@ __FBSDID("$FreeBSD$");
>>>    #include<sys/resource.h>
>>>    #include<sys/socket.h>
>>>
>>> +#include<elf.h>
>>>    #include<errno.h>
>>>    #include<limits.h>
>>>    #include<paths.h>
>>> @@ -51,6 +52,7 @@ __FBSDID("$FreeBSD$");
>>>
>>>    #include "../stdlib/atexit.h"
>>>    #include "tzfile.h"		/* from ../../../contrib/tzcode/stdtime */
>>> +#include "libc_private.h"
>>>
>>>    #define	_PATH_ZONEINFO	TZDIR	/* from tzfile.h */
>>>
>>> @@ -585,6 +587,8 @@ yesno:
>>>
>>>    	case _SC_NPROCESSORS_CONF:
>>>    	case _SC_NPROCESSORS_ONLN:
>>> +		if (_elf_aux_info(AT_NCPUS,&value, sizeof(value)) == 0)
>>> +			return ((long)value);
>>>    		mib[0] = CTL_HW;
>>>    		mib[1] = HW_NCPU;
>>>    		break;
>>>
>> Will this make controlling the number of CPU online or CPU hotplug
>> be impossible on FreeBSD ?
> If I think about hotplug CPUs I can think of other 1000
> problems/races/bad situations to be fixed before this one, really.
These are problems only in kernel, but kib's change is about ABI
between userland and kernel, I hope we don't introduce an ABI which
is not extendable road stone.

> Attilio
>
>