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Date:      Thu, 1 Sep 2011 16:58:31 +0200
From:      Ivan Voras <ivoras@freebsd.org>
To:        Attilio Rao <attilio@freebsd.org>
Cc:        "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>, Sean Bruno <seanbru@yahoo-inc.com>
Subject:   Re: Large machine test ideas
Message-ID:  <CAF-QHFUCYJL28GxQu_=QjGgiBOVumNK56tO2rnmmTo4%2B%2Bjf0yw@mail.gmail.com>
In-Reply-To: <CAJ-FndCbXs0btQUc8_L3F4kcsdu5WN-75HY%2BhdKY%2B5OGhase2Q@mail.gmail.com>
References:  <j38lj5$s9a$1@dough.gmane.org> <CAMBSHm_Sv_KZUs4h-tDGAZCq8s2qo_bMmfZxLbVkcH1=_Wu0OQ@mail.gmail.com> <CAF-QHFW=aU3=iKE9WMg6%2BD6eP9OXth=c0AidBc140ykmAPD2zg@mail.gmail.com> <201108291415.32605.jhb@freebsd.org> <j3ju8s$kuo$2@dough.gmane.org> <1314818323.2610.6.camel@hitfishpass-lx.corp.yahoo.com> <CAJ-FndCbXs0btQUc8_L3F4kcsdu5WN-75HY%2BhdKY%2B5OGhase2Q@mail.gmail.com>

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On 1 September 2011 16:11, Attilio Rao <attilio@freebsd.org> wrote:

>> I mean, if we have 2 cpus in a machine, but MAXCPU is set to 256, there
>> is a bunch of "lost" memory and higher levels of lock contention?
>>
>> I thought that attilio was taking a stab at enhancing this, but at the
>> current time anything more than a value of 64 for MAXCPU is kind of a
>> "caveat emptor" area of FreeBSD.
>
> With newest current you can redefine MAXCPU in your kernel config, so
> you don't need to bump the default value.
> I think 64 as default value is good enough.
>
> Removing MAXCPU dependency from the KBI is an important project
> someone should adopt and bring to conclusion.

That's certainly one half of it and thanks for the work, but the real
question in this thread is what Sean asked: what are the negative
side-effects of simply bumping MAXCPU to 256 by default? AFAIK, there
are not that many structures which are statically sized by MAXCMPU and
most use the runtime-detected smp_cpus?



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