Re: [patch] SMP alternatives

From: H. Peter Anvin
Date: Wed Nov 23 2005 - 17:25:58 EST

Andi Kleen wrote:
On Wed, Nov 23, 2005 at 02:15:24PM -0800, Linus Torvalds wrote:

On Wed, 23 Nov 2005, Andi Kleen wrote:

THAT is what I'd like to have CPU support for. Not for UP (it's going away), and not for the kernel (it's never single-threaded).

There is one reasonly interesting special case that will probably stay
around: single CPU guest in a virtualized environment.

.. and then the _virtualizer_ should just set the bit.

That wouldn't work if it's limited limited to ring 3.

Also currently at least the Xen the driver interfaces seem to rely on lock, but perhaps that can be changed.

Well, with VTX or Pacifica virtualization is in ring 3. The fact that Xen isn't is a workaround for current hardware, so when we're talking about new hardware it's pointless.

What you really want is one bit for kernel mode (cpl 0-2) and one for user mode (cpl 3).

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