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. Thanks. -Fenghua
