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Subject: Re: svn commit: r242402 - in head/sys: kern vm
From: Adrian Chadd <adrian@freebsd.org>
To: attilio@freebsd.org
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On 31 October 2012 11:33, Attilio Rao <attilio@freebsd.org> wrote:

>> Doesn't this padding to cache line size only help x86 processors in an
>> SMP kernel?  I was expecting to see some #ifdef SMP so that we don't pay
>> a big price for no gain in small-memory ARM systems and such.  But maybe
>> I'm misunderstanding the reason for the padding.
>
> I didn't want to do this because this would be meaning that SMP option
> may become a completely killer for modules/kernel ABI compatibility.

Right, but you didn't make it configurable for us embedded peeps who
still care about memory usage.

> Also, if you look at the modified list of locks I don't think they
> should be too much, I hardly believe ARM UP is going to hurt that much
> from loosing some padding in tdq structures or callout.

There's a few million more embedded MIPS boards out there with
16mb/32mb of RAM than target PCs for FreeBSD.

Would you mind making the padding part configurable and just default
it to "do the padding" ?
That way for the atheros MIPS builds I can turn it off and save on the
memory overhead.

Thanks,


Adrian