Re: [PATCH v2 0/8] Introduce a huge-page pre-zeroing mechanism

[dan.j.williams]

David Hildenbrand (Red Hat) wrote:
[..]
> > Give me a list of 1Gig pages and this stuff becomes much more efficient
> > than anything the CPU can do.
> 
> Right, and ideally we'd implement any such mechanisms in a way that more 
> parts of the kernel can benefit, and not just an unloved in-memory 
> file-system that most people just want to get rid of as soon as we can :)

CPUs have tended to eat the value of simple DMA offload operations like
copy/zero over time.

In the case of this patch there is no async-offload benefit because
userspace is already charged with spawning more threads if it wants more
parallelism.

For sync-offload one engine may be able to beat a single CPU, but now
you have created bandwidth contention problems with a component that is
less responsive to the scheduler.

Call me skeptical.

Signed, someone with async_tx and dmaengine battle scars.