Manoj, Can you elaborate on this information I received: "The register acts like an adder in that every write adds to the previously written value minus anything the device has consumed."
I assume this is talking about the SLIST_BAOFF_DBELL register. In regards to the test case, if the register is an adder and every write adds to the previously written value, why would we expect the second read to be the same as the first read when a write is performed in between them? -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1563375 Title: A a single PCI read or write appears twice on the PCIe bus. This happens when using the SR-IOV feature with Cavium's liquidIO card Status in linux package in Ubuntu: In Progress Bug description: Cavium engineers are testing SR-IOV feature with Cavium's new liquidIO card (based on OCTEON processor running as an intelligent NIC) on x86 Dell servers and ran into the issue described below. They are *not* seeing this issue on Intel 82599 NIC. So far, they have seen this on multiple Dell servers - T5810 & Dell T630 (x86 - Ubuntu certified). We are testing a Cavium OCTEON device in EP mode with SRIOV. With a CentOS7 VM running on the Ubuntu 14.04.2 host (using VFIO) we see that a single PCI read or write transaction targeting the device’s BAR0 issued from the VM appears twice on the PCIe bus. The same accesses work fine when the VF is accessed directly from the Ubuntu 14.04.2 host. These BAR0 PCI accesses do not require a driver on the VM side. We can reproduce the problem using a simple user-space application to access the VF’s BAR0 registers. We do not see this problem when the VM runs within a CentOS 7 host or under a Ubuntu 12.04 host. This appears specific to Ubuntu 14.04 release. Appreciate your help in any clues or pointers to this behavior. This issue is also not happening with 16.04 beta. Steps to reproduce the bug with pcimem: Read: ./pcimem /sys/bus/pci/devices/0000\:04\:00.0/resource0 0x10080 d Write: ./pcimem /sys/bus/pci/devices/0000\:04\:00.0/resource0 0x10080 d 2048 Read again: ./pcimem /sys/bus/pci/devices/0000\:04\:00.0/resource0 0x10080 d The value of SLIST_BAOFF_DBELL should be the same for the first read and the second read, after the write. If the bug is hit, the second read will report a value of double instead of the same. The register should have read back the same value that was written. The register acts like an adder in that every write adds to the previously written value minus anything the device has consumed. We see that the second read returns double the value written in the single write. We captured a PCIe trace and found that each of the PCI operation accessing this register is seen twice on the PCI bus. The 2 writes cause the register value to double which has implications for normal operation. The PCIe trace is attached and has markers to identify the relevant transactions. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1563375/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
