diff options
authorSiobhan Butler <>2015-03-22 13:25:07 +0000
committerThomas Monjalon <>2015-03-31 03:21:41 +0200
commita73a9510ebcbab995ef89d324a309fe04b487e1c (patch)
parentef7d28668505a04afe0f93f097f58614679c0f9f (diff)
doc: update faq
Added some of the questions posted to the mailing list to the FAQ section of release notes. Signed-off-by: Siobhan Butler <>
1 files changed, 35 insertions, 0 deletions
diff --git a/doc/guides/rel_notes/faq.rst b/doc/guides/rel_notes/faq.rst
index 054db10..14b1167 100644
--- a/doc/guides/rel_notes/faq.rst
+++ b/doc/guides/rel_notes/faq.rst
@@ -191,3 +191,38 @@ In this case, this has to be done manually on the VM host, using the following c
where <interface> being the interface providing the virtual functions for example, eth0, <VF function> being the virtual function number, for example 0,
and <MAC address> being the desired MAC address.
+Is it safe to add an entry to the hash table while running?
+Currently the table implementation is not a thread safe implementation and assumes that locking between threads and processes is handled by the user's application.
+This is likely to be supported in future releases.
+What is the purpose of setting iommu=pt?
+DPDK uses a 1:1 mapping and does not support IOMMU. IOMMU allows for simpler VM physical address translation.
+The second role of IOMMU is to allow protection from unwanted memory access by an unsafe device that has DMA privileges.
+Unfortunately, the protection comes with an extremely high perfomance cost for high speed NICs.
+iommu=pt disables IOMMU support for the hypervisor.
+When trying to send packets from an application to itself, meaning smac==dmac, using Intel(R) 82599 VF packets are lost.
+Check on register LLE(PFVMTXSSW[n]), which allows an individual pool to send traffic and have it looped back to itself.
+Can I split packet RX to use DPDK and have an application's higher order functions continue using Linux* pthread?
+The DPDK's lcore threads are Linux* pthreads bound onto specific cores. Configure the DPDK to do work on the same
+cores and run the application's other work on other cores using the DPDK's "coremask" setting to specify which
+cores it should launch itself on.
+Is it possible to exchange data between DPDK processes and regular userspace processes via some shared memory or IPC mechanism?
+Yes - DPDK processes are regular Linux/BSD processes, and can use all OS provided IPC mechanisms.
+Can the multiple queues in Intel(R) I350 be used with DPDK?
+I350 has RSS support and 8 queue pairs can be used in RSS mode. It should work with multi-queue DPDK applications using RSS.
+How can hugepage-backed memory be shared among multiple processes?
+See the Primary and Secondary examples in the multi-process sample application.