[+cc Ashok] On Wed, Sep 29, 2021 at 01:40:41PM -0700, Eric Pilmore wrote: > I am curious to know if anybody working with Ice Lake has seen this > behavior where the MemRD TLPs, from a "cpu(s)" issuing I/O Reads > to an I/O device, are carrying varying RequesterID (RID) values that > don't represent any enumerated devices (per lspci) in the system? > The particular system in use is a Supermicro box with 2 CPU sockets, > each socket comprised of a 16 core (2 thread/core) processor. I have > not seen any correlation between issuing the I/O Read operation from > a particular core and the RID that shows up in the respective MemRD > TLP. Normally, I would have expected the RID to have been either 0x0000 > or the BDF of the respective Root Port into which the device being > read was plugged into. > > I assume this behavior is intended to increase I/O bandwidth and reduce > latency by allowing even more outstanding I/O Reads than is normally > afforded by the (per-device) Tag field of a MemRD TLP. > > I have been searching around, but having trouble finding specifics about > this behavior in any specs or micro-architecture documents. If anybody > knows of any pointers it would be greatly appreciated. I don't know anything about this. Added Ashok in case he can shed any light.
