Date: Mon, 27 Sep 2010 19:41:09 +0200 From: Attilio Rao <attilio@freebsd.org> To: Sean Bruno <seanbru@yahoo-inc.com> Cc: "sbruno@freebsd.org" <sbruno@freebsd.org>, "current@freebsd.org" <current@freebsd.org> Subject: Re: MAXCPU preparations Message-ID: <AANLkTini=hUrGq3dMcksf45E1q8MPpdhnkhr-gA0sW5-@mail.gmail.com> In-Reply-To: <1285604516.7245.16.camel@home-yahoo> References: <1285601161.7245.7.camel@home-yahoo> <4CA0BE08.50408@freebsd.org> <1285604516.7245.16.camel@home-yahoo>
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2010/9/27 Sean Bruno <seanbru@yahoo-inc.com>:
> On Mon, 2010-09-27 at 08:53 -0700, Julian Elischer wrote:
>> On 9/27/10 8:26 AM, Sean Bruno wrote:
>> > Does this look like an appropriate modification to libmemstat?
>> >
>> > Sean
>> >
>> >
>> > =3D=3D=3D=3D //depot/yahoo/ybsd_7/src/lib/libmemstat/memstat.h#4
>> > - /home/seanbru/ybsd_7/src/lib/libmemstat/memstat.h =3D=3D=3D=3D
>> > @@ -28,12 +28,13 @@
>> >
>> > =C2=A0 #ifndef _MEMSTAT_H_
>> > =C2=A0 #define =C2=A0 =C2=A0 =C2=A0 =C2=A0_MEMSTAT_H_
>> > +#include<sys/param.h>
>> >
>> > =C2=A0 /*
>> > =C2=A0 =C2=A0* Number of CPU slots in library-internal data structures=
. =C2=A0This
>> > should be
>> > =C2=A0 =C2=A0* at least the value of MAXCPU from param.h.
>> > =C2=A0 =C2=A0*/
>> > -#define =C2=A0 =C2=A0 =C2=A0 =C2=A0MEMSTAT_MAXCPU =C2=A064
>> > +#define =C2=A0 =C2=A0 =C2=A0 =C2=A0MEMSTAT_MAXCPU =C2=A0MAXCPU /* def=
ined in
>> > sys/${ARCH}/include/param.h */
>> >
>>
>>
>> wouldn't it be better to do a sysctlbyname() and use the real value
>> for the system?
>>
>
> That was my initial thought (as prodded by scottl and peter).
>
> If it is made dynamic, could this be opening a race condition where the
> call to sysctlbyname() returns a count of CPUS that is in turn changed
> by the offlining of a CPU? =C2=A0Or am I thinking to much about this?
We still can't support CPU hotplugging so the easy answer is 'don't
bother about variadic CPUs number'.
I don't really know what libmemstat is willing to do with that macro
(and I don't have time to look at it now) maybe you could shade a
light about what's its usage? Does it really needs to know MAXCPUS or
just wants a large enough value to fill anything?
Thanks,
Attilio
--=20
Peace can only be achieved by understanding - A. Einstein
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