Re: [RFC PATCH 1/8] x86/cpufeatures: Enumerate MOVDIRI instruction

[Thomas Gleixner]

On Tue, 19 Jun 2018, Fenghua Yu wrote:

> On Tue, Jun 19, 2018 at 10:57:44AM +0200, Thomas Gleixner wrote:
> > On Fri, 15 Jun 2018, Fenghua Yu wrote:
> > 
> > > MOVDIRI moves doubleword or quadword from register to memory through
> > > direct store which is implemented by using write combining (WC) for
> > > writing data directly into memory without caching the data.
> > 
> > And that is useful for what?
> 
> Programmable agents can handle streaming offload (e.g. high speed packet
> processing in network). Hardware implements a doorbell (tail pointer)
> register that is updated by software when adding new work-elements to
> the streaming offload work-queue.
> 
> MOVDIRI can be used as the doorbell write which is a 4-byte or 8-byte
> uncachable write to MMIO. MOVDIRI has lower overhead than other ways
> to write the doorbell.
> 
> In low latency offload (e.g. Non-Volatile Memory, etc), MOVDIR64B writes
> work descriptors (and data in some cases) to device-hosted work-queues
> with atomicity.

Makes sense, but why is this not part of the changelog ?

Thanks,

	tglx