svn commit: r242402 - in head/sys: kern vm

[Jim Harris]

On Wed, Oct 31, 2012 at 12:30 PM, Peter Jeremy <peter at rulingia.com> wrote:

> On 2012-Oct-31 18:57:37 +0000, Attilio Rao <attilio at FreeBSD.org> wrote:
> >On 10/31/12, Adrian Chadd <adrian at freebsd.org> wrote:
> >> Right, but you didn't make it configurable for us embedded peeps who
> >> still care about memory usage.
> >
> >How is this possible without breaking the module/kernel ABI?
>
> Memory usage may override ABI compatibility in an embedded environment.
>
> >All that assuming you can actually prove a real performance loss even
> >in the new cases.
>
> The issue with padding on embedded systems is memory utilisation rather
> than performance.


Agree that for embedded systems, we need to be careful about proliferating
this throughout the entire kernel.

But for the usages thus far, Attilio is right that they should not affect
UP.  The ULE and callout changes made very recently are on per-CPU data
structures, so for UP, that's padding just one mutex each.

For the vpglock->mtx_padalign conversion, this is functionally a nop.
vpglock was already doing this padding.

-Jim