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Date:      Thu, 1 Nov 2012 14:05:44 +0000
From:      Attilio Rao <attilio@freebsd.org>
To:        Ian Lepore <freebsd@damnhippie.dyndns.org>
Cc:        svn-src-head@freebsd.org, svn-src-all@freebsd.org, Gleb Smirnoff <glebius@freebsd.org>, src-committers@freebsd.org
Subject:   Re: svn commit: r242402 - in head/sys: kern vm
Message-ID:  <CAJ-FndCpcBTFpsdTLYoadG2P3oZFYq_viGSTNOc7YM5G66FFsg@mail.gmail.com>
In-Reply-To: <1351778472.1120.117.camel@revolution.hippie.lan>
References:  <201210311807.q9VI7IcX000993@svn.freebsd.org> <CAJ-FndDRkBS57e9mzZoJWX5ugJ0KBGxhMSO50KB8Wm8MFudjCA@mail.gmail.com> <1351707964.1120.97.camel@revolution.hippie.lan> <CAJ-FndC7QwpNAjzQTumqTY6Sj_RszXPwc0pbHv2-pRGMqbw0ww@mail.gmail.com> <20121101100814.GB70741@FreeBSD.org> <CAJ-FndARMhgCRYwo0%2BS4tZ=At6rHJSz_tsy-OtHRHZKkxL-sig@mail.gmail.com> <1351778472.1120.117.camel@revolution.hippie.lan>

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On Thu, Nov 1, 2012 at 2:01 PM, Ian Lepore
<freebsd@damnhippie.dyndns.org> wrote:
> On Thu, 2012-11-01 at 10:42 +0000, Attilio Rao wrote:
>> On 11/1/12, Gleb Smirnoff <glebius@freebsd.org> wrote:
>> > On Wed, Oct 31, 2012 at 06:33:51PM +0000, Attilio Rao wrote:
>> > A> > Doesn't this padding to cache line size only help x86 processors in an
>> > A> > SMP kernel?  I was expecting to see some #ifdef SMP so that we don't
>> > pay
>> > A> > a big price for no gain in small-memory ARM systems and such.  But
>> > maybe
>> > A> > I'm misunderstanding the reason for the padding.
>> > A>
>> > A> I didn't want to do this because this would be meaning that SMP option
>> > A> may become a completely killer for modules/kernel ABI compatibility.
>> >
>> > Do we support loading non-SMP modules on SMP kernel and vice versa?
>>
>> Actually that's my point, we do.
>>
>> Attilio
>>
>>
>
> Well we've got other similar problems lurking then.  What about a module
> compiled on an arm system that had #define CACHE_LINE_SIZE 32 and then
> it gets run on a different arm system whose kernel is compiled with
> #define CACHE_LINE_SIZE 64?

That should not happen. Is that a real case where you build a module
for an ARM family and want to run against a kernel compiled for
another?

CACHE_LINE_SIZE must not change during a STABLE release lifetime, of
course, for the same arch.

Attilio


-- 
Peace can only be achieved by understanding - A. Einstein



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