Re: [PATCH 0/5] x86: Impplement support for unaccepted memory

On 8/10/21 10:31 AM, Kirill A. Shutemov wrote:

On Tue, Aug 10, 2021 at 08:51:01AM -0700, Dave Hansen wrote:

quoted

Let's say we have a 128GB VM.  How much does faster does this approach
reach userspace than if all memory was accepted up front?  How much
memory _could_ have been accepted at the point userspace starts running?

Acceptance code is not optimized yet: we accept memory in 4k chunk which
is very slow because hypercall overhead dominates the picture.

As of now, kernel boot time of 1 VCPU and 64TiB VM with upfront memory
accept is >20 times slower than with this lazy memory accept approach.

That's a pretty big deal.

The difference is going to be substantially lower once we get it optimized
properly.

What does this mean?  Is this future work in the kernel or somewhere in
the TDX hardware/firmware which will speed things up?